From: Muchun Song <hidden> Date: 2021-02-04 03:54:35
Hi all,
This patch series will free some vmemmap pages(struct page structures)
associated with each hugetlbpage when preallocated to save memory.
In order to reduce the difficulty of the first version of code review.
From this version, we disable PMD/huge page mapping of vmemmap if this
feature was enabled. This accutualy eliminate a bunch of the complex code
doing page table manipulation. When this patch series is solid, we cam add
the code of vmemmap page table manipulation in the future.
The struct page structures (page structs) are used to describe a physical
page frame. By default, there is a one-to-one mapping from a page frame to
it's corresponding page struct.
The HugeTLB pages consist of multiple base page size pages and is supported
by many architectures. See hugetlbpage.rst in the Documentation directory
for more details. On the x86 architecture, HugeTLB pages of size 2MB and 1GB
are currently supported. Since the base page size on x86 is 4KB, a 2MB
HugeTLB page consists of 512 base pages and a 1GB HugeTLB page consists of
4096 base pages. For each base page, there is a corresponding page struct.
Within the HugeTLB subsystem, only the first 4 page structs are used to
contain unique information about a HugeTLB page. HUGETLB_CGROUP_MIN_ORDER
provides this upper limit. The only 'useful' information in the remaining
page structs is the compound_head field, and this field is the same for all
tail pages.
By removing redundant page structs for HugeTLB pages, memory can returned to
the buddy allocator for other uses.
When the system boot up, every 2M HugeTLB has 512 struct page structs which
size is 8 pages(sizeof(struct page) * 512 / PAGE_SIZE).
HugeTLB struct pages(8 pages) page frame(8 pages)
+-----------+ ---virt_to_page---> +-----------+ mapping to +-----------+
| | | 0 | -------------> | 0 |
| | +-----------+ +-----------+
| | | 1 | -------------> | 1 |
| | +-----------+ +-----------+
| | | 2 | -------------> | 2 |
| | +-----------+ +-----------+
| | | 3 | -------------> | 3 |
| | +-----------+ +-----------+
| | | 4 | -------------> | 4 |
| 2MB | +-----------+ +-----------+
| | | 5 | -------------> | 5 |
| | +-----------+ +-----------+
| | | 6 | -------------> | 6 |
| | +-----------+ +-----------+
| | | 7 | -------------> | 7 |
| | +-----------+ +-----------+
| |
| |
| |
+-----------+
The value of page->compound_head is the same for all tail pages. The first
page of page structs (page 0) associated with the HugeTLB page contains the 4
page structs necessary to describe the HugeTLB. The only use of the remaining
pages of page structs (page 1 to page 7) is to point to page->compound_head.
Therefore, we can remap pages 2 to 7 to page 1. Only 2 pages of page structs
will be used for each HugeTLB page. This will allow us to free the remaining
6 pages to the buddy allocator.
Here is how things look after remapping.
HugeTLB struct pages(8 pages) page frame(8 pages)
+-----------+ ---virt_to_page---> +-----------+ mapping to +-----------+
| | | 0 | -------------> | 0 |
| | +-----------+ +-----------+
| | | 1 | -------------> | 1 |
| | +-----------+ +-----------+
| | | 2 | ----------------^ ^ ^ ^ ^ ^
| | +-----------+ | | | | |
| | | 3 | ------------------+ | | | |
| | +-----------+ | | | |
| | | 4 | --------------------+ | | |
| 2MB | +-----------+ | | |
| | | 5 | ----------------------+ | |
| | +-----------+ | |
| | | 6 | ------------------------+ |
| | +-----------+ |
| | | 7 | --------------------------+
| | +-----------+
| |
| |
| |
+-----------+
When a HugeTLB is freed to the buddy system, we should allocate 6 pages for
vmemmap pages and restore the previous mapping relationship.
Apart from 2MB HugeTLB page, we also have 1GB HugeTLB page. It is similar
to the 2MB HugeTLB page. We also can use this approach to free the vmemmap
pages.
In this case, for the 1GB HugeTLB page, we can save 4094 pages. This is a
very substantial gain. On our server, run some SPDK/QEMU applications which
will use 1024GB hugetlbpage. With this feature enabled, we can save ~16GB
(1G hugepage)/~12GB (2MB hugepage) memory.
Because there are vmemmap page tables reconstruction on the freeing/allocating
path, it increases some overhead. Here are some overhead analysis.
1) Allocating 10240 2MB hugetlb pages.
a) With this patch series applied:
# time echo 10240 > /proc/sys/vm/nr_hugepages
real 0m0.166s
user 0m0.000s
sys 0m0.166s
# bpftrace -e 'kprobe:alloc_fresh_huge_page { @start[tid] = nsecs; } kretprobe:alloc_fresh_huge_page /@start[tid]/ { @latency = hist(nsecs - @start[tid]); delete(@start[tid]); }'
Attaching 2 probes...
@latency:
[8K, 16K) 8360 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[16K, 32K) 1868 |@@@@@@@@@@@ |
[32K, 64K) 10 | |
[64K, 128K) 2 | |
b) Without this patch series:
# time echo 10240 > /proc/sys/vm/nr_hugepages
real 0m0.066s
user 0m0.000s
sys 0m0.066s
# bpftrace -e 'kprobe:alloc_fresh_huge_page { @start[tid] = nsecs; } kretprobe:alloc_fresh_huge_page /@start[tid]/ { @latency = hist(nsecs - @start[tid]); delete(@start[tid]); }'
Attaching 2 probes...
@latency:
[4K, 8K) 10176 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[8K, 16K) 62 | |
[16K, 32K) 2 | |
Summarize: this feature is about ~2x slower than before.
2) Freeing 10240 2MB hugetlb pages.
a) With this patch series applied:
# time echo 0 > /proc/sys/vm/nr_hugepages
real 0m0.004s
user 0m0.000s
sys 0m0.002s
# bpftrace -e 'kprobe:__free_hugepage { @start[tid] = nsecs; } kretprobe:__free_hugepage /@start[tid]/ { @latency = hist(nsecs - @start[tid]); delete(@start[tid]); }'
Attaching 2 probes...
@latency:
[16K, 32K) 10240 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
b) Without this patch series:
# time echo 0 > /proc/sys/vm/nr_hugepages
real 0m0.077s
user 0m0.001s
sys 0m0.075s
# bpftrace -e 'kprobe:__free_hugepage { @start[tid] = nsecs; } kretprobe:__free_hugepage /@start[tid]/ { @latency = hist(nsecs - @start[tid]); delete(@start[tid]); }'
Attaching 2 probes...
@latency:
[4K, 8K) 9950 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[8K, 16K) 287 |@ |
[16K, 32K) 3 | |
Summarize: The overhead of __free_hugepage is about ~2-4x slower than before.
But according to the allocation test above, I think that here is
also ~2x slower than before.
But why the 'real' time of patched is smaller than before? Because
In this patch series, the freeing hugetlb is asynchronous(through
kwoker).
Although the overhead has increased, the overhead is not significant. Like Mike
said, "However, remember that the majority of use cases create hugetlb pages at
or shortly after boot time and add them to the pool. So, additional overhead is
at pool creation time. There is no change to 'normal run time' operations of
getting a page from or returning a page to the pool (think page fault/unmap)".
Todo:
- Free all of the tail vmemmap pages
Now for the 2MB HugrTLB page, we only free 6 vmemmap pages. we really can
free 7 vmemmap pages. In this case, we can see 8 of the 512 struct page
structures has beed set PG_head flag. If we can adjust compound_head()
slightly and make compound_head() return the real head struct page when
the parameter is the tail struct page but with PG_head flag set.
In order to make the code evolution route clearer. This feature can can be
a separate patch after this patchset is solid.
- Support for other architectures (e.g. aarch64).
- Enable PMD/huge page mapping of vmemmap even if this feature was enabled.
Changelog in v13 -> v14:
- Refuse to free the HugeTLB page when the system is under memory pressure.
- Use GFP_ATOMIC to allocate vmemmap pages instead of GFP_KERNEL.
- Rebase to linux-next 20210202.
- Fix and add some comments for vmemmap_remap_free().
Thanks to Oscar, Mike, David H and David R's suggestions and review.
Changelog in v12 -> v13:
- Remove VM_WARN_ON_PAGE macro.
- Add more comments in vmemmap_pte_range() and vmemmap_remap_free().
Thanks to Oscar and Mike's suggestions and review.
Changelog in v11 -> v12:
- Move VM_WARN_ON_PAGE to a separate patch.
- Call __free_hugepage() with hugetlb_lock (See patch #5.) to serialize
with dissolve_free_huge_page(). It is to prepare for patch #9.
- Introduce PageHugeInflight. See patch #9.
Changelog in v10 -> v11:
- Fix compiler error when !CONFIG_HUGETLB_PAGE_FREE_VMEMMAP.
- Rework some comments and commit changes.
- Rework vmemmap_remap_free() to 3 parameters.
Thanks to Oscar and Mike's suggestions and review.
Changelog in v9 -> v10:
- Fix a bug in patch #11. Thanks to Oscar for pointing that out.
- Rework some commit log or comments. Thanks Mike and Oscar for the suggestions.
- Drop VMEMMAP_TAIL_PAGE_REUSE in the patch #3.
Thank you very much Mike and Oscar for reviewing the code.
Changelog in v8 -> v9:
- Rework some code. Very thanks to Oscar.
- Put all the non-hugetlb vmemmap functions under sparsemem-vmemmap.c.
Changelog in v7 -> v8:
- Adjust the order of patches.
Very thanks to David and Oscar. Your suggestions are very valuable.
Changelog in v6 -> v7:
- Rebase to linux-next 20201130
- Do not use basepage mapping for vmemmap when this feature is disabled.
- Rework some patchs.
[PATCH v6 08/16] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page
[PATCH v6 10/16] mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb page
Thanks to Oscar and Barry.
Changelog in v5 -> v6:
- Disable PMD/huge page mapping of vmemmap if this feature was enabled.
- Simplify the first version code.
Changelog in v4 -> v5:
- Rework somme comments and code in the [PATCH v4 04/21] and [PATCH v4 05/21].
Thanks to Mike and Oscar's suggestions.
Changelog in v3 -> v4:
- Move all the vmemmap functions to hugetlb_vmemmap.c.
- Make the CONFIG_HUGETLB_PAGE_FREE_VMEMMAP default to y, if we want to
disable this feature, we should disable it by a boot/kernel command line.
- Remove vmemmap_pgtable_{init, deposit, withdraw}() helper functions.
- Initialize page table lock for vmemmap through core_initcall mechanism.
Thanks for Mike and Oscar's suggestions.
Changelog in v2 -> v3:
- Rename some helps function name. Thanks Mike.
- Rework some code. Thanks Mike and Oscar.
- Remap the tail vmemmap page with PAGE_KERNEL_RO instead of PAGE_KERNEL.
Thanks Matthew.
- Add some overhead analysis in the cover letter.
- Use vmemap pmd table lock instead of a hugetlb specific global lock.
Changelog in v1 -> v2:
- Fix do not call dissolve_compound_page in alloc_huge_page_vmemmap().
- Fix some typo and code style problems.
- Remove unused handle_vmemmap_fault().
- Merge some commits to one commit suggested by Mike.
Muchun Song (8):
mm: memory_hotplug: factor out bootmem core functions to
bootmem_info.c
mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP
mm: hugetlb: free the vmemmap pages associated with each HugeTLB page
mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap
mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate
mm: hugetlb: gather discrete indexes of tail page
mm: hugetlb: optimize the code with the help of the compiler
Documentation/admin-guide/kernel-parameters.txt | 14 ++
Documentation/admin-guide/mm/hugetlbpage.rst | 3 +
arch/x86/mm/init_64.c | 13 +-
fs/Kconfig | 6 +
include/linux/bootmem_info.h | 65 +++++
include/linux/hugetlb.h | 43 +++-
include/linux/hugetlb_cgroup.h | 19 +-
include/linux/memory_hotplug.h | 27 --
include/linux/mm.h | 5 +
mm/Makefile | 2 +
mm/bootmem_info.c | 124 ++++++++++
mm/hugetlb.c | 23 +-
mm/hugetlb_vmemmap.c | 314 ++++++++++++++++++++++++
mm/hugetlb_vmemmap.h | 33 +++
mm/memory_hotplug.c | 116 ---------
mm/sparse-vmemmap.c | 280 +++++++++++++++++++++
mm/sparse.c | 1 +
17 files changed, 930 insertions(+), 158 deletions(-)
create mode 100644 include/linux/bootmem_info.h
create mode 100644 mm/bootmem_info.c
create mode 100644 mm/hugetlb_vmemmap.c
create mode 100644 mm/hugetlb_vmemmap.h
--
2.11.0
From: Muchun Song <hidden> Date: 2021-02-04 03:55:35
The option HUGETLB_PAGE_FREE_VMEMMAP allows for the freeing of
some vmemmap pages associated with pre-allocated HugeTLB pages.
For example, on X86_64 6 vmemmap pages of size 4KB each can be
saved for each 2MB HugeTLB page. 4094 vmemmap pages of size 4KB
each can be saved for each 1GB HugeTLB page.
When a HugeTLB page is allocated or freed, the vmemmap array
representing the range associated with the page will need to be
remapped. When a page is allocated, vmemmap pages are freed
after remapping. When a page is freed, previously discarded
vmemmap pages must be allocated before remapping.
The config option is introduced early so that supporting code
can be written to depend on the option. The initial version of
the code only provides support for x86-64.
Like other code which frees vmemmap, this config option depends on
HAVE_BOOTMEM_INFO_NODE. The routine register_page_bootmem_info() is
used to register bootmem info. Therefore, make sure
register_page_bootmem_info is enabled if HUGETLB_PAGE_FREE_VMEMMAP
is defined.
Signed-off-by: Muchun Song <redacted>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Mike Kravetz <redacted>
---
arch/x86/mm/init_64.c | 2 +-
fs/Kconfig | 6 ++++++
2 files changed, 7 insertions(+), 1 deletion(-)
From: Muchun Song <hidden> Date: 2021-02-04 03:55:35
Move bootmem info registration common API to individual bootmem_info.c.
And we will use {get,put}_page_bootmem() to initialize the page for the
vmemmap pages or free the vmemmap pages to buddy in the later patch.
So move them out of CONFIG_MEMORY_HOTPLUG_SPARSE. This is just code
movement without any functional change.
Signed-off-by: Muchun Song <redacted>
Acked-by: Mike Kravetz <redacted>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: David Hildenbrand <redacted>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
---
arch/x86/mm/init_64.c | 3 +-
include/linux/bootmem_info.h | 40 +++++++++++++
include/linux/memory_hotplug.h | 27 ---------
mm/Makefile | 1 +
mm/bootmem_info.c | 124 +++++++++++++++++++++++++++++++++++++++++
mm/memory_hotplug.c | 116 --------------------------------------
mm/sparse.c | 1 +
7 files changed, 168 insertions(+), 144 deletions(-)
create mode 100644 include/linux/bootmem_info.h
create mode 100644 mm/bootmem_info.c
@@ -1571,7 +1572,7 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,returnerr;}-#if defined(CONFIG_MEMORY_HOTPLUG_SPARSE) && defined(CONFIG_HAVE_BOOTMEM_INFO_NODE)+#ifdef CONFIG_HAVE_BOOTMEM_INFO_NODEvoidregister_page_bootmem_memmap(unsignedlongsection_nr,structpage*start_page,unsignedlongnr_pages){
@@ -18,18 +18,6 @@ struct vmem_altmap;#ifdef CONFIG_MEMORY_HOTPLUGstructpage*pfn_to_online_page(unsignedlongpfn);-/*-*Typesforfreebootmemstoredinpage->lru.next.Thesehavetobein-*somerandomrangeinunsignedlongspacefordebuggingpurposes.-*/-enum{-MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE=12,-SECTION_INFO=MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE,-MIX_SECTION_INFO,-NODE_INFO,-MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE=NODE_INFO,-};-/* Types for control the zone type of onlined and offlined memory */enum{/* Offline the memory. */
From: Muchun Song <hidden> Date: 2021-02-04 03:55:57
Every HugeTLB has more than one struct page structure. We __know__ that
we only use the first 4(HUGETLB_CGROUP_MIN_ORDER) struct page structures
to store metadata associated with each HugeTLB.
There are a lot of struct page structures associated with each HugeTLB
page. For tail pages, the value of compound_head is the same. So we can
reuse first page of tail page structures. We map the virtual addresses
of the remaining pages of tail page structures to the first tail page
struct, and then free these page frames. Therefore, we need to reserve
two pages as vmemmap areas.
When we allocate a HugeTLB page from the buddy, we can free some vmemmap
pages associated with each HugeTLB page. It is more appropriate to do it
in the prep_new_huge_page().
The free_vmemmap_pages_per_hpage(), which indicates how many vmemmap
pages associated with a HugeTLB page can be freed, returns zero for
now, which means the feature is disabled. We will enable it once all
the infrastructure is there.
Signed-off-by: Muchun Song <redacted>
---
include/linux/bootmem_info.h | 27 +++++-
include/linux/mm.h | 3 +
mm/Makefile | 1 +
mm/hugetlb.c | 3 +
mm/hugetlb_vmemmap.c | 219 +++++++++++++++++++++++++++++++++++++++++++
mm/hugetlb_vmemmap.h | 20 ++++
mm/sparse-vmemmap.c | 207 ++++++++++++++++++++++++++++++++++++++++
7 files changed, 479 insertions(+), 1 deletion(-)
create mode 100644 mm/hugetlb_vmemmap.c
create mode 100644 mm/hugetlb_vmemmap.h
@@ -27,8 +27,215 @@#include<linux/spinlock.h>#include<linux/vmalloc.h>#include<linux/sched.h>+#include<linux/pgtable.h>+#include<linux/bootmem_info.h>+#include<asm/dma.h>#include<asm/pgalloc.h>+#include<asm/tlbflush.h>++/**+*vmemmap_remap_walk-walkvmemmappagetable+*+*@remap_pte:calledforeachnon-emptyPTE(lowest-level)entry.+*@reuse_page:thepagewhichisreusedforthetailvmemmappages.+*@reuse_addr:thevirtualaddressofthe@reuse_pagepage.+*@vmemmap_pages:thelistheadofthevmemmappagesthatcanbefreed.+*/+structvmemmap_remap_walk{+void(*remap_pte)(pte_t*pte,unsignedlongaddr,+structvmemmap_remap_walk*walk);+structpage*reuse_page;+unsignedlongreuse_addr;+structlist_head*vmemmap_pages;+};++staticvoidvmemmap_pte_range(pmd_t*pmd,unsignedlongaddr,+unsignedlongend,+structvmemmap_remap_walk*walk)+{+pte_t*pte;++pte=pte_offset_kernel(pmd,addr);++/*+*Thereuse_pageisfound'first'intablewalkbeforewestart+*remapping(whichiscalling@walk->remap_pte).+*/+if(!walk->reuse_page){+BUG_ON(pte_none(*pte)||walk->reuse_addr!=addr);++walk->reuse_page=pte_page(*pte++);+/*+*Becausethereuseaddressispartoftherangethatweare+*walking,skipthereuseaddressrange.+*/+addr+=PAGE_SIZE;+}++for(;addr!=end;addr+=PAGE_SIZE,pte++){+BUG_ON(pte_none(*pte));++walk->remap_pte(pte,addr,walk);+}+}++staticvoidvmemmap_pmd_range(pud_t*pud,unsignedlongaddr,+unsignedlongend,+structvmemmap_remap_walk*walk)+{+pmd_t*pmd;+unsignedlongnext;++pmd=pmd_offset(pud,addr);+do{+BUG_ON(pmd_none(*pmd)||pmd_leaf(*pmd));++next=pmd_addr_end(addr,end);+vmemmap_pte_range(pmd,addr,next,walk);+}while(pmd++,addr=next,addr!=end);+}++staticvoidvmemmap_pud_range(p4d_t*p4d,unsignedlongaddr,+unsignedlongend,+structvmemmap_remap_walk*walk)+{+pud_t*pud;+unsignedlongnext;++pud=pud_offset(p4d,addr);+do{+BUG_ON(pud_none(*pud));++next=pud_addr_end(addr,end);+vmemmap_pmd_range(pud,addr,next,walk);+}while(pud++,addr=next,addr!=end);+}++staticvoidvmemmap_p4d_range(pgd_t*pgd,unsignedlongaddr,+unsignedlongend,+structvmemmap_remap_walk*walk)+{+p4d_t*p4d;+unsignedlongnext;++p4d=p4d_offset(pgd,addr);+do{+BUG_ON(p4d_none(*p4d));++next=p4d_addr_end(addr,end);+vmemmap_pud_range(p4d,addr,next,walk);+}while(p4d++,addr=next,addr!=end);+}++staticvoidvmemmap_remap_range(unsignedlongstart,unsignedlongend,+structvmemmap_remap_walk*walk)+{+unsignedlongaddr=start;+unsignedlongnext;+pgd_t*pgd;++VM_BUG_ON(!IS_ALIGNED(start,PAGE_SIZE));+VM_BUG_ON(!IS_ALIGNED(end,PAGE_SIZE));++pgd=pgd_offset_k(addr);+do{+BUG_ON(pgd_none(*pgd));++next=pgd_addr_end(addr,end);+vmemmap_p4d_range(pgd,addr,next,walk);+}while(pgd++,addr=next,addr!=end);++/*+*Wedonotchangethemappingofthevmemmapvirtualaddressrange+*[@start,@start+PAGE_SIZE)whichbelongstothereuserange.+*SowenotneedtoflushtheTLB.+*/+flush_tlb_kernel_range(start+PAGE_SIZE,end);+}++/*+*Freeavmemmappage.Avmemmappagecanbeallocatedfromthememblock+*allocatororbuddyallocator.IfthePG_reservedflagisset,itmeans+*thatitallocatedfromthememblockallocator,justfreeitviathe+*free_bootmem_page().Otherwise,use__free_page().+*/+staticinlinevoidfree_vmemmap_page(structpage*page)+{+if(PageReserved(page))+free_bootmem_page(page);+else+__free_page(page);+}++/* Free a list of the vmemmap pages */+staticvoidfree_vmemmap_page_list(structlist_head*list)+{+structpage*page,*next;++list_for_each_entry_safe(page,next,list,lru){+list_del(&page->lru);+free_vmemmap_page(page);+}+}++staticvoidvmemmap_remap_pte(pte_t*pte,unsignedlongaddr,+structvmemmap_remap_walk*walk)+{+/*+*Remapthetailpagesasread-onlytocatchillegalwriteoperation+*tothetailpages.+*/+pgprot_tpgprot=PAGE_KERNEL_RO;+pte_tentry=mk_pte(walk->reuse_page,pgprot);+structpage*page=pte_page(*pte);++list_add(&page->lru,walk->vmemmap_pages);+set_pte_at(&init_mm,addr,pte,entry);+}++/**+*vmemmap_remap_free-remapthevmemmapvirtualaddressrange[@start,@end)+*tothepagewhich@reuseismappedto,thenfreevmemmap+*whichtherangearemappedto.+*@start:startaddressofthevmemmapvirtualaddressrangethatwewant+*toremap.+*@end:endaddressofthevmemmapvirtualaddressrangethatwewantto+*remap.+*@reuse:reuseaddress.+*+*Note:Thisfunctiondependsonvmemmapbeingbasepagemapped.Pleasemake+*surethatthearchitecturedisablesPMDmappingofvmemmappageswhencalling+*thisfunction.+*/+voidvmemmap_remap_free(unsignedlongstart,unsignedlongend,+unsignedlongreuse)+{+LIST_HEAD(vmemmap_pages);+structvmemmap_remap_walkwalk={+.remap_pte=vmemmap_remap_pte,+.reuse_addr=reuse,+.vmemmap_pages=&vmemmap_pages,+};++/*+*Inordertomakeremappingroutinemostefficientforthehugepages,+*theroutineofvmemmappagetablewalkinghasthefollowingrules+*(seemoredetailsfromthevmemmap_pte_range()):+*+*-Therange[@start,@end)andtherange[@reuse,@reuse+PAGE_SIZE)+*shouldbecontinuous.+*-The@reuseaddressispartoftherange[@reuse,@end)thatweare+*walkingwhichispassedtovmemmap_remap_range().+*-The@reuseaddressisthefirstinthecompleterange.+*+*Soweneedtomakesurethat@startand@reusemeettheaboverules.+*/+BUG_ON(start-reuse!=PAGE_SIZE);++vmemmap_remap_range(reuse,end,&walk);+free_vmemmap_page_list(&vmemmap_pages);+}/**Allocateablockofmemorytobeusedtobackthevirtualmemorymap
From: Muchun Song <hidden> Date: 2021-02-04 03:56:36
When we free a HugeTLB page to the buddy allocator, we should allocate the
vmemmap pages associated with it. But we may cannot allocate vmemmap pages
when the system is under memory pressure, in this case, we just refuse to
free the HugeTLB page instead of looping forever trying to allocate the
pages.
Signed-off-by: Muchun Song <redacted>
---
include/linux/mm.h | 2 ++
mm/hugetlb.c | 19 ++++++++++++-
mm/hugetlb_vmemmap.c | 30 +++++++++++++++++++++
mm/hugetlb_vmemmap.h | 8 ++++++
mm/sparse-vmemmap.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++-
5 files changed, 132 insertions(+), 2 deletions(-)
@@ -1397,16 +1397,26 @@ static void __free_huge_page(struct page *page)h->resv_huge_pages++;if(HPageTemporary(page)){-list_del(&page->lru);ClearHPageTemporary(page);++if(alloc_huge_page_vmemmap(h,page,GFP_ATOMIC)){+h->surplus_huge_pages++;+h->surplus_huge_pages_node[nid]++;+gotoenqueue;+}+list_del(&page->lru);update_and_free_page(h,page);}elseif(h->surplus_huge_pages_node[nid]){+if(alloc_huge_page_vmemmap(h,page,GFP_ATOMIC))+gotoenqueue;+/* remove the page from active list */list_del(&page->lru);update_and_free_page(h,page);h->surplus_huge_pages--;h->surplus_huge_pages_node[nid]--;}else{+enqueue:arch_clear_hugepage_flags(page);enqueue_huge_page(h,page);}
@@ -237,6 +238,78 @@ void vmemmap_remap_free(unsigned long start, unsigned long end,free_vmemmap_page_list(&vmemmap_pages);}+staticvoidvmemmap_restore_pte(pte_t*pte,unsignedlongaddr,+structvmemmap_remap_walk*walk)+{+pgprot_tpgprot=PAGE_KERNEL;+structpage*page;+void*to;++BUG_ON(pte_page(*pte)!=walk->reuse_page);++page=list_first_entry(walk->vmemmap_pages,structpage,lru);+list_del(&page->lru);+to=page_to_virt(page);+copy_page(to,(void*)walk->reuse_addr);++set_pte_at(&init_mm,addr,pte,mk_pte(page,pgprot));+}++staticintalloc_vmemmap_page_list(unsignedlongstart,unsignedlongend,+gfp_tgfp_mask,structlist_head*list)+{+unsignedlongaddr;+intnid=page_to_nid((constvoid*)start);+structpage*page,*next;++for(addr=start;addr<end;addr+=PAGE_SIZE){+page=alloc_pages_node(nid,gfp_mask,0);+if(!page)+gotoout;+list_add_tail(&page->lru,list);+}++return0;+out:+list_for_each_entry_safe(page,next,list,lru)+__free_pages(page,0);+return-ENOMEM;+}++/**+*vmemmap_remap_alloc-remapthevmemmapvirtualaddressrange[@start,end)+*tothepagewhichisfromthe@vmemmap_pages+*respectively.+*@start:startaddressofthevmemmapvirtualaddressrangethatwewant+*toremap.+*@end:endaddressofthevmemmapvirtualaddressrangethatwewantto+*remap.+*@reuse:reuseaddress.+*@gpf_mask:GFPflagforallocatingvmemmappages.+*/+intvmemmap_remap_alloc(unsignedlongstart,unsignedlongend,+unsignedlongreuse,gfp_tgfp_mask)+{+LIST_HEAD(vmemmap_pages);+structvmemmap_remap_walkwalk={+.remap_pte=vmemmap_restore_pte,+.reuse_addr=reuse,+.vmemmap_pages=&vmemmap_pages,+};++/* See the comment in the vmemmap_remap_free(). */+BUG_ON(start-reuse!=PAGE_SIZE);++might_sleep_if(gfpflags_allow_blocking(gfp_mask));++if(alloc_vmemmap_page_list(start,end,gfp_mask,&vmemmap_pages))+return-ENOMEM;++vmemmap_remap_range(reuse,end,&walk);++return0;+}+/**Allocateablockofmemorytobeusedtobackthevirtualmemorymap*ortobackthepagetablesthatareusedtocreatethemapping.
From: Muchun Song <hidden> Date: 2021-02-04 03:56:36
For HugeTLB page, there are more metadata to save in the struct page.
But the head struct page cannot meet our needs, so we have to abuse
other tail struct page to store the metadata. In order to avoid
conflicts caused by subsequent use of more tail struct pages, we can
gather these discrete indexes of tail struct page. In this case, it
will be easier to add a new tail page index later.
There are only (RESERVE_VMEMMAP_SIZE / sizeof(struct page)) struct
page structs that can be used when CONFIG_HUGETLB_PAGE_FREE_VMEMMAP,
so add a BUILD_BUG_ON to catch invalid usage of the tail struct page.
Signed-off-by: Muchun Song <redacted>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
---
include/linux/hugetlb.h | 20 ++++++++++++++++++--
include/linux/hugetlb_cgroup.h | 19 +++++++++++--------
mm/hugetlb_vmemmap.c | 8 ++++++++
3 files changed, 37 insertions(+), 10 deletions(-)
From: Muchun Song <hidden> Date: 2021-02-04 03:58:29
We cannot optimize if a "struct page" crosses page boundaries. If
it is true, we can optimize the code with the help of a compiler.
When free_vmemmap_pages_per_hpage() returns zero, most functions are
optimized by the compiler.
Signed-off-by: Muchun Song <redacted>
---
include/linux/hugetlb.h | 3 ++-
mm/hugetlb_vmemmap.c | 13 +++++++++++++
2 files changed, 15 insertions(+), 1 deletion(-)
From: Muchun Song <hidden> Date: 2021-02-04 03:58:29
All the infrastructure is ready, so we introduce nr_free_vmemmap_pages
field in the hstate to indicate how many vmemmap pages associated with
a HugeTLB page that can be freed to buddy allocator. And initialize it
in the hugetlb_vmemmap_init(). This patch is actual enablement of the
feature.
Signed-off-by: Muchun Song <redacted>
Acked-by: Mike Kravetz <redacted>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
---
include/linux/hugetlb.h | 3 +++
mm/hugetlb.c | 1 +
mm/hugetlb_vmemmap.c | 30 ++++++++++++++++++++++++++----
mm/hugetlb_vmemmap.h | 5 +++++
4 files changed, 35 insertions(+), 4 deletions(-)
From: Muchun Song <hidden> Date: 2021-02-04 03:58:29
Add a kernel parameter hugetlb_free_vmemmap to enable the feature of
freeing unused vmemmap pages associated with each hugetlb page on boot.
We disables PMD mapping of vmemmap pages for x86-64 arch when this
feature is enabled. Because vmemmap_remap_free() depends on vmemmap
being base page mapped.
Signed-off-by: Muchun Song <redacted>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Barry Song <redacted>
---
Documentation/admin-guide/kernel-parameters.txt | 14 ++++++++++++++
Documentation/admin-guide/mm/hugetlbpage.rst | 3 +++
arch/x86/mm/init_64.c | 8 ++++++--
include/linux/hugetlb.h | 19 +++++++++++++++++++
mm/hugetlb_vmemmap.c | 22 ++++++++++++++++++++++
5 files changed, 64 insertions(+), 2 deletions(-)
@@ -1577,6 +1577,20 @@ Documentation/admin-guide/mm/hugetlbpage.rst. Format: size[KMG]+ hugetlb_free_vmemmap=+ [KNL] When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set,+ this controls freeing unused vmemmap pages associated+ with each HugeTLB page. When this option is enabled,+ we disable PMD/huge page mapping of vmemmap pages which+ increase page table pages. So if a user/sysadmin only+ uses a small number of HugeTLB pages (as a percentage+ of system memory), they could end up using more memory+ with hugetlb_free_vmemmap on as opposed to off.+ Format: { on | off (default) }++ on: enable the feature+ off: disable the feature+ hung_task_panic= [KNL] Should the hung task detector generate panics. Format: 0 | 1
@@ -145,6 +145,9 @@ default_hugepagesz will all result in 256 2M huge pages being allocated. Valid default huge page size is architecture dependent.+hugetlb_free_vmemmap+ When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, this enables freeing+ unused vmemmap pages associated with each HugeTLB page. When multiple huge page sizes are supported, ``/proc/sys/vm/nr_hugepages`` indicates the current number of pre-allocated huge pages of the default size.
@@ -1557,7 +1558,8 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,{interr;-if(end-start<PAGES_PER_SECTION*sizeof(structpage))+if((is_hugetlb_free_vmemmap_enabled()&&!altmap)||+end-start<PAGES_PER_SECTION*sizeof(structpage))err=vmemmap_populate_basepages(start,end,node,NULL);elseif(boot_cpu_has(X86_FEATURE_PSE))err=vmemmap_populate_hugepages(start,end,node,altmap);
@@ -1585,6 +1587,8 @@ void register_page_bootmem_memmap(unsigned long section_nr,pmd_t*pmd;unsignedintnr_pmd_pages;structpage*page;+boolbase_mapping=!boot_cpu_has(X86_FEATURE_PSE)||+is_hugetlb_free_vmemmap_enabled();for(;addr<end;addr=next){pte_t*pte=NULL;
@@ -1610,7 +1614,7 @@ void register_page_bootmem_memmap(unsigned long section_nr,}get_page_bootmem(section_nr,pud_page(*pud),MIX_SECTION_INFO);-if(!boot_cpu_has(X86_FEATURE_PSE)){+if(base_mapping){next=(addr+PAGE_SIZE)&PAGE_MASK;pmd=pmd_offset(pud,addr);if(pmd_none(*pmd))
From: Miaohe Lin <linmiaohe@huawei.com> Date: 2021-02-04 06:34:53
On 2021/2/4 11:50, Muchun Song wrote:
We cannot optimize if a "struct page" crosses page boundaries. If
it is true, we can optimize the code with the help of a compiler.
When free_vmemmap_pages_per_hpage() returns zero, most functions are
optimized by the compiler.
Signed-off-by: Muchun Song <redacted>
I like it. Thanks.
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
From: Miaohe Lin <linmiaohe@huawei.com> Date: 2021-02-04 11:45:08
Hi:
On 2021/2/4 11:50, Muchun Song wrote:
The option HUGETLB_PAGE_FREE_VMEMMAP allows for the freeing of
some vmemmap pages associated with pre-allocated HugeTLB pages.
For example, on X86_64 6 vmemmap pages of size 4KB each can be
saved for each 2MB HugeTLB page. 4094 vmemmap pages of size 4KB
each can be saved for each 1GB HugeTLB page.
When a HugeTLB page is allocated or freed, the vmemmap array
representing the range associated with the page will need to be
remapped. When a page is allocated, vmemmap pages are freed
after remapping. When a page is freed, previously discarded
vmemmap pages must be allocated before remapping.
The config option is introduced early so that supporting code
can be written to depend on the option. The initial version of
the code only provides support for x86-64.
Like other code which frees vmemmap, this config option depends on
HAVE_BOOTMEM_INFO_NODE. The routine register_page_bootmem_info() is
used to register bootmem info. Therefore, make sure
register_page_bootmem_info is enabled if HUGETLB_PAGE_FREE_VMEMMAP
is defined.
Signed-off-by: Muchun Song <redacted>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Mike Kravetz <redacted>
LGTM. Thanks.
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
From: Miaohe Lin <linmiaohe@huawei.com> Date: 2021-02-05 07:26:22
Hi:
On 2021/2/4 11:50, Muchun Song wrote:
Add a kernel parameter hugetlb_free_vmemmap to enable the feature of
freeing unused vmemmap pages associated with each hugetlb page on boot.
We disables PMD mapping of vmemmap pages for x86-64 arch when this
feature is enabled. Because vmemmap_remap_free() depends on vmemmap
being base page mapped.
Signed-off-by: Muchun Song <redacted>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Barry Song <redacted>
Looks good to me. Thanks.
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
@@ -1577,6 +1577,20 @@ Documentation/admin-guide/mm/hugetlbpage.rst. Format: size[KMG]+ hugetlb_free_vmemmap=+ [KNL] When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set,+ this controls freeing unused vmemmap pages associated+ with each HugeTLB page. When this option is enabled,+ we disable PMD/huge page mapping of vmemmap pages which+ increase page table pages. So if a user/sysadmin only+ uses a small number of HugeTLB pages (as a percentage+ of system memory), they could end up using more memory+ with hugetlb_free_vmemmap on as opposed to off.+ Format: { on | off (default) }++ on: enable the feature+ off: disable the feature+ hung_task_panic= [KNL] Should the hung task detector generate panics. Format: 0 | 1
@@ -145,6 +145,9 @@ default_hugepagesz will all result in 256 2M huge pages being allocated. Valid default huge page size is architecture dependent.+hugetlb_free_vmemmap+ When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, this enables freeing+ unused vmemmap pages associated with each HugeTLB page. When multiple huge page sizes are supported, ``/proc/sys/vm/nr_hugepages`` indicates the current number of pre-allocated huge pages of the default size.
@@ -1557,7 +1558,8 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,{interr;-if(end-start<PAGES_PER_SECTION*sizeof(structpage))+if((is_hugetlb_free_vmemmap_enabled()&&!altmap)||+end-start<PAGES_PER_SECTION*sizeof(structpage))err=vmemmap_populate_basepages(start,end,node,NULL);elseif(boot_cpu_has(X86_FEATURE_PSE))err=vmemmap_populate_hugepages(start,end,node,altmap);
@@ -1585,6 +1587,8 @@ void register_page_bootmem_memmap(unsigned long section_nr,pmd_t*pmd;unsignedintnr_pmd_pages;structpage*page;+boolbase_mapping=!boot_cpu_has(X86_FEATURE_PSE)||+is_hugetlb_free_vmemmap_enabled();for(;addr<end;addr=next){pte_t*pte=NULL;
@@ -1610,7 +1614,7 @@ void register_page_bootmem_memmap(unsigned long section_nr,}get_page_bootmem(section_nr,pud_page(*pud),MIX_SECTION_INFO);-if(!boot_cpu_has(X86_FEATURE_PSE)){+if(base_mapping){next=(addr+PAGE_SIZE)&PAGE_MASK;pmd=pmd_offset(pud,addr);if(pmd_none(*pmd))
From: Miaohe Lin <linmiaohe@huawei.com> Date: 2021-02-05 07:31:10
On 2021/2/4 11:50, Muchun Song wrote:
quoted hunk
All the infrastructure is ready, so we introduce nr_free_vmemmap_pages
field in the hstate to indicate how many vmemmap pages associated with
a HugeTLB page that can be freed to buddy allocator. And initialize it
in the hugetlb_vmemmap_init(). This patch is actual enablement of the
feature.
Signed-off-by: Muchun Song <redacted>
Acked-by: Mike Kravetz <redacted>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
---
include/linux/hugetlb.h | 3 +++
mm/hugetlb.c | 1 +
mm/hugetlb_vmemmap.c | 30 ++++++++++++++++++++++++++----
mm/hugetlb_vmemmap.h | 5 +++++
4 files changed, 35 insertions(+), 4 deletions(-)
Not a problem. Should we set h->nr_free_vmemmap_pages to 0 in 'else' case explicitly ?
Anyway, looks good to me. Thanks.
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
From: Miaohe Lin <linmiaohe@huawei.com> Date: 2021-02-05 07:32:15
On 2021/2/4 11:50, Muchun Song wrote:
For HugeTLB page, there are more metadata to save in the struct page.
But the head struct page cannot meet our needs, so we have to abuse
other tail struct page to store the metadata. In order to avoid
conflicts caused by subsequent use of more tail struct pages, we can
gather these discrete indexes of tail struct page. In this case, it
will be easier to add a new tail page index later.
There are only (RESERVE_VMEMMAP_SIZE / sizeof(struct page)) struct
page structs that can be used when CONFIG_HUGETLB_PAGE_FREE_VMEMMAP,
so add a BUILD_BUG_ON to catch invalid usage of the tail struct page.
Signed-off-by: Muchun Song <redacted>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Thanks.
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Not a problem. Should we set h->nr_free_vmemmap_pages to 0 in 'else' case explicitly ?
No, hstate fields are already zeroed.
I know hstate fields are already zeroed. What I mean is should we set nr_free_vmemmap_pages
to 0 _explicitly_ like nr_huge_pages and free_huge_pages in hugetlb_add_hstate() ?
But this is really trival.
Many thanks for reply.
From: Oscar Salvador <osalvador@suse.de> Date: 2021-02-05 08:55:35
On Thu, Feb 04, 2021 at 11:50:38AM +0800, Muchun Song wrote:
Every HugeTLB has more than one struct page structure. We __know__ that
we only use the first 4(HUGETLB_CGROUP_MIN_ORDER) struct page structures
to store metadata associated with each HugeTLB.
There are a lot of struct page structures associated with each HugeTLB
page. For tail pages, the value of compound_head is the same. So we can
reuse first page of tail page structures. We map the virtual addresses
of the remaining pages of tail page structures to the first tail page
struct, and then free these page frames. Therefore, we need to reserve
two pages as vmemmap areas.
When we allocate a HugeTLB page from the buddy, we can free some vmemmap
pages associated with each HugeTLB page. It is more appropriate to do it
in the prep_new_huge_page().
The free_vmemmap_pages_per_hpage(), which indicates how many vmemmap
pages associated with a HugeTLB page can be freed, returns zero for
now, which means the feature is disabled. We will enable it once all
the infrastructure is there.
Signed-off-by: Muchun Song <redacted>
---
[...]
+void free_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+ unsigned long vmemmap_addr = (unsigned long)head;
+ unsigned long vmemmap_end, vmemmap_reuse;
+
+ if (!free_vmemmap_pages_per_hpage(h))
+ return;
+
+ vmemmap_addr += RESERVE_VMEMMAP_SIZE;
+ vmemmap_end = vmemmap_addr + free_vmemmap_pages_size_per_hpage(h);
+ vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
+
+ /*
+ * Remap the vmemmap virtual address range [@vmemmap_addr, @vmemmap_end)
+ * to the page which @vmemmap_reuse is mapped to, then free the vmemmap
+ * pages which the range are mapped to.
"then free the pages which the range [@vmemmap_addr, @vmemmap_end] is mapped to."
I am not a native but sounds better to me.
Well, we BUG_ON on empty PTE, so not sure that pointing out here is worth.
It sounds like we do nothing when it's empty.
Maybe:
"called for each lowest-level entry (PTE)"
+ * @reuse_page: the page which is reused for the tail vmemmap pages.
+ * @reuse_addr: the virtual address of the @reuse_page page.
+ * @vmemmap_pages: the list head of the vmemmap pages that can be freed.
+ */
+struct vmemmap_remap_walk {
+ void (*remap_pte)(pte_t *pte, unsigned long addr,
+ struct vmemmap_remap_walk *walk);
+ struct page *reuse_page;
+ unsigned long reuse_addr;
+ struct list_head *vmemmap_pages;
+};
+
+static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
+ unsigned long end,
+ struct vmemmap_remap_walk *walk)
+{
+ pte_t *pte;
+
+ pte = pte_offset_kernel(pmd, addr);
+
+ /*
+ * The reuse_page is found 'first' in table walk before we start
+ * remapping (which is calling @walk->remap_pte).
+ */
+ if (!walk->reuse_page) {
+ BUG_ON(pte_none(*pte) || walk->reuse_addr != addr);
I would rather have them in separate lines:
BUG_ON(pte_none(*pte));
BUG_ON(walk->reuse_addr != addr));
It helps when trying to figure out when we explode. One could dig in the
registers, but let's make it easier to find out.
+
[...]
+static void vmemmap_remap_range(unsigned long start, unsigned long end,
+ struct vmemmap_remap_walk *walk)
+{
+ unsigned long addr = start;
+ unsigned long next;
+ pgd_t *pgd;
+
+ VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE));
+ VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE));
+
+ pgd = pgd_offset_k(addr);
+ do {
+ BUG_ON(pgd_none(*pgd));
+
+ next = pgd_addr_end(addr, end);
+ vmemmap_p4d_range(pgd, addr, next, walk);
+ } while (pgd++, addr = next, addr != end);
+
+ /*
+ * We do not change the mapping of the vmemmap virtual address range
+ * [@start, @start + PAGE_SIZE) which belongs to the reuse range.
+ * So we not need to flush the TLB.
+ */
+ flush_tlb_kernel_range(start + PAGE_SIZE, end);
I find that comment a bit confusing. I would rather describe what are we
flushing instead of what we are not.
+}
+
+/*
+ * Free a vmemmap page. A vmemmap page can be allocated from the memblock
+ * allocator or buddy allocator. If the PG_reserved flag is set, it means
+ * that it allocated from the memblock allocator, just free it via the
+ * free_bootmem_page(). Otherwise, use __free_page().
+ */
+static inline void free_vmemmap_page(struct page *page)
+{
+ if (PageReserved(page))
+ free_bootmem_page(page);
+ else
+ __free_page(page);
+}
+
+/* Free a list of the vmemmap pages */
+static void free_vmemmap_page_list(struct list_head *list)
+{
+ struct page *page, *next;
+
+ list_for_each_entry_safe(page, next, list, lru) {
+ list_del(&page->lru);
+ free_vmemmap_page(page);
+ }
+}
+
+static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
+ struct vmemmap_remap_walk *walk)
+{
+ /*
+ * Remap the tail pages as read-only to catch illegal write operation
+ * to the tail pages.
+ */
+ pgprot_t pgprot = PAGE_KERNEL_RO;
+ pte_t entry = mk_pte(walk->reuse_page, pgprot);
+ struct page *page = pte_page(*pte);
+
+ list_add(&page->lru, walk->vmemmap_pages);
+ set_pte_at(&init_mm, addr, pte, entry);
+}
+
+/**
+ * vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
+ * to the page which @reuse is mapped to, then free vmemmap
+ * which the range are mapped to.
+ * @start: start address of the vmemmap virtual address range that we want
+ * to remap.
+ * @end: end address of the vmemmap virtual address range that we want to
+ * remap.
+ * @reuse: reuse address.
+ *
+ * Note: This function depends on vmemmap being base page mapped. Please make
+ * sure that the architecture disables PMD mapping of vmemmap pages when calling
+ * this function.
Well, we do not really depend on the architecture to not map the vmemmap range
with PMDs, right? IIUC, that is driven by your boot parameter (patch#5), which
overrides whatever the architecture can do.
Functional changes look good to me, so with all the above fixes, you can add:
Reviewed-by: Oscar Salvador <osalvador@suse.de>
--
Oscar Salvador
SUSE L3
Not a problem. Should we set h->nr_free_vmemmap_pages to 0 in 'else' case explicitly ?
No, hstate fields are already zeroed.
I know hstate fields are already zeroed. What I mean is should we set nr_free_vmemmap_pages
to 0 _explicitly_ like nr_huge_pages and free_huge_pages in hugetlb_add_hstate() ?
But this is really trival.
From: Oscar Salvador <osalvador@suse.de> Date: 2021-02-05 09:00:36
On Thu, Feb 04, 2021 at 11:50:35AM +0800, Muchun Song wrote:
Changelog in v13 -> v14:
- Refuse to free the HugeTLB page when the system is under memory pressure.
- Use GFP_ATOMIC to allocate vmemmap pages instead of GFP_KERNEL.
- Rebase to linux-next 20210202.
- Fix and add some comments for vmemmap_remap_free().
Thanks to Oscar, Mike, David H and David R's suggestions and review.
Changelog in v12 -> v13:
- Remove VM_WARN_ON_PAGE macro.
- Add more comments in vmemmap_pte_range() and vmemmap_remap_free().
Thanks to Oscar and Mike's suggestions and review.
Changelog in v11 -> v12:
- Move VM_WARN_ON_PAGE to a separate patch.
- Call __free_hugepage() with hugetlb_lock (See patch #5.) to serialize
with dissolve_free_huge_page(). It is to prepare for patch #9.
- Introduce PageHugeInflight. See patch #9.
Changelog in v10 -> v11:
- Fix compiler error when !CONFIG_HUGETLB_PAGE_FREE_VMEMMAP.
- Rework some comments and commit changes.
- Rework vmemmap_remap_free() to 3 parameters.
Thanks to Oscar and Mike's suggestions and review.
Changelog in v9 -> v10:
- Fix a bug in patch #11. Thanks to Oscar for pointing that out.
- Rework some commit log or comments. Thanks Mike and Oscar for the suggestions.
- Drop VMEMMAP_TAIL_PAGE_REUSE in the patch #3.
Thank you very much Mike and Oscar for reviewing the code.
Changelog in v8 -> v9:
- Rework some code. Very thanks to Oscar.
- Put all the non-hugetlb vmemmap functions under sparsemem-vmemmap.c.
Changelog in v7 -> v8:
- Adjust the order of patches.
Very thanks to David and Oscar. Your suggestions are very valuable.
Changelog in v6 -> v7:
- Rebase to linux-next 20201130
- Do not use basepage mapping for vmemmap when this feature is disabled.
- Rework some patchs.
[PATCH v6 08/16] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page
[PATCH v6 10/16] mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb page
Thanks to Oscar and Barry.
Changelog in v5 -> v6:
- Disable PMD/huge page mapping of vmemmap if this feature was enabled.
- Simplify the first version code.
Changelog in v4 -> v5:
- Rework somme comments and code in the [PATCH v4 04/21] and [PATCH v4 05/21].
Thanks to Mike and Oscar's suggestions.
Changelog in v3 -> v4:
- Move all the vmemmap functions to hugetlb_vmemmap.c.
- Make the CONFIG_HUGETLB_PAGE_FREE_VMEMMAP default to y, if we want to
disable this feature, we should disable it by a boot/kernel command line.
- Remove vmemmap_pgtable_{init, deposit, withdraw}() helper functions.
- Initialize page table lock for vmemmap through core_initcall mechanism.
Thanks for Mike and Oscar's suggestions.
Changelog in v2 -> v3:
- Rename some helps function name. Thanks Mike.
- Rework some code. Thanks Mike and Oscar.
- Remap the tail vmemmap page with PAGE_KERNEL_RO instead of PAGE_KERNEL.
Thanks Matthew.
- Add some overhead analysis in the cover letter.
- Use vmemap pmd table lock instead of a hugetlb specific global lock.
Changelog in v1 -> v2:
- Fix do not call dissolve_compound_page in alloc_huge_page_vmemmap().
- Fix some typo and code style problems.
- Remove unused handle_vmemmap_fault().
- Merge some commits to one commit suggested by Mike.
Muchun Song (8):
mm: memory_hotplug: factor out bootmem core functions to
bootmem_info.c
mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP
mm: hugetlb: free the vmemmap pages associated with each HugeTLB page
mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap
mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate
mm: hugetlb: gather discrete indexes of tail page
mm: hugetlb: optimize the code with the help of the compiler
Documentation/admin-guide/kernel-parameters.txt | 14 ++
Documentation/admin-guide/mm/hugetlbpage.rst | 3 +
arch/x86/mm/init_64.c | 13 +-
fs/Kconfig | 6 +
include/linux/bootmem_info.h | 65 +++++
include/linux/hugetlb.h | 43 +++-
include/linux/hugetlb_cgroup.h | 19 +-
include/linux/memory_hotplug.h | 27 --
include/linux/mm.h | 5 +
mm/Makefile | 2 +
mm/bootmem_info.c | 124 ++++++++++
mm/hugetlb.c | 23 +-
mm/hugetlb_vmemmap.c | 314 ++++++++++++++++++++++++
mm/hugetlb_vmemmap.h | 33 +++
mm/memory_hotplug.c | 116 ---------
mm/sparse-vmemmap.c | 280 +++++++++++++++++++++
mm/sparse.c | 1 +
17 files changed, 930 insertions(+), 158 deletions(-)
create mode 100644 include/linux/bootmem_info.h
create mode 100644 mm/bootmem_info.c
create mode 100644 mm/hugetlb_vmemmap.c
create mode 100644 mm/hugetlb_vmemmap.h
--
2.11.0
From: Oscar Salvador <osalvador@suse.de> Date: 2021-02-05 09:13:33
On Thu, Feb 04, 2021 at 11:50:43AM +0800, Muchun Song wrote:
We cannot optimize if a "struct page" crosses page boundaries. If
it is true, we can optimize the code with the help of a compiler.
When free_vmemmap_pages_per_hpage() returns zero, most functions are
optimized by the compiler.
"When the "struct page size" crosses page boundaries we cannot
make use of this feature.
Let free_vmemmap_pages_per_hpage() return zero if that is the case,
most of the functions can be optimized away."
I think the above is more clear, but just a suggestion.
Not a problem. Should we set h->nr_free_vmemmap_pages to 0 in 'else' case explicitly ?
No, hstate fields are already zeroed.
I know hstate fields are already zeroed. What I mean is should we set nr_free_vmemmap_pages
to 0 _explicitly_ like nr_huge_pages and free_huge_pages in hugetlb_add_hstate() ?
But this is really trival.
From: Muchun Song <hidden> Date: 2021-02-05 09:21:08
On Fri, Feb 5, 2021 at 5:09 PM Oscar Salvador [off-list ref] wrote:
On Thu, Feb 04, 2021 at 11:50:43AM +0800, Muchun Song wrote:
quoted
We cannot optimize if a "struct page" crosses page boundaries. If
it is true, we can optimize the code with the help of a compiler.
When free_vmemmap_pages_per_hpage() returns zero, most functions are
optimized by the compiler.
"When the "struct page size" crosses page boundaries we cannot
make use of this feature.
Let free_vmemmap_pages_per_hpage() return zero if that is the case,
most of the functions can be optimized away."
I think the above is more clear, but just a suggestion.
From: Muchun Song <hidden> Date: 2021-02-05 09:33:14
On Thu, Feb 4, 2021 at 11:54 AM Muchun Song [off-list ref] wrote:
quoted hunk
When we free a HugeTLB page to the buddy allocator, we should allocate the
vmemmap pages associated with it. But we may cannot allocate vmemmap pages
when the system is under memory pressure, in this case, we just refuse to
free the HugeTLB page instead of looping forever trying to allocate the
pages.
Signed-off-by: Muchun Song <redacted>
---
include/linux/mm.h | 2 ++
mm/hugetlb.c | 19 ++++++++++++-
mm/hugetlb_vmemmap.c | 30 +++++++++++++++++++++
mm/hugetlb_vmemmap.h | 8 ++++++
mm/sparse-vmemmap.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++-
5 files changed, 132 insertions(+), 2 deletions(-)
@@ -1397,16 +1397,26 @@ static void __free_huge_page(struct page *page)h->resv_huge_pages++;if(HPageTemporary(page)){-list_del(&page->lru);ClearHPageTemporary(page);++if(alloc_huge_page_vmemmap(h,page,GFP_ATOMIC)){+h->surplus_huge_pages++;+h->surplus_huge_pages_node[nid]++;+gotoenqueue;+}+list_del(&page->lru);update_and_free_page(h,page);}elseif(h->surplus_huge_pages_node[nid]){+if(alloc_huge_page_vmemmap(h,page,GFP_ATOMIC))+gotoenqueue;+/* remove the page from active list */list_del(&page->lru);update_and_free_page(h,page);h->surplus_huge_pages--;h->surplus_huge_pages_node[nid]--;}else{+enqueue:arch_clear_hugepage_flags(page);enqueue_huge_page(h,page);}
@@ -237,6 +238,78 @@ void vmemmap_remap_free(unsigned long start, unsigned long end,free_vmemmap_page_list(&vmemmap_pages);}+staticvoidvmemmap_restore_pte(pte_t*pte,unsignedlongaddr,+structvmemmap_remap_walk*walk)+{+pgprot_tpgprot=PAGE_KERNEL;+structpage*page;+void*to;++BUG_ON(pte_page(*pte)!=walk->reuse_page);++page=list_first_entry(walk->vmemmap_pages,structpage,lru);+list_del(&page->lru);+to=page_to_virt(page);+copy_page(to,(void*)walk->reuse_addr);++set_pte_at(&init_mm,addr,pte,mk_pte(page,pgprot));+}++staticintalloc_vmemmap_page_list(unsignedlongstart,unsignedlongend,+gfp_tgfp_mask,structlist_head*list)+{+unsignedlongaddr;+intnid=page_to_nid((constvoid*)start);+structpage*page,*next;++for(addr=start;addr<end;addr+=PAGE_SIZE){+page=alloc_pages_node(nid,gfp_mask,0);+if(!page)+gotoout;+list_add_tail(&page->lru,list);+}++return0;+out:+list_for_each_entry_safe(page,next,list,lru)+__free_pages(page,0);+return-ENOMEM;+}++/**+*vmemmap_remap_alloc-remapthevmemmapvirtualaddressrange[@start,end)+*tothepagewhichisfromthe@vmemmap_pages+*respectively.+*@start:startaddressofthevmemmapvirtualaddressrangethatwewant+*toremap.+*@end:endaddressofthevmemmapvirtualaddressrangethatwewantto+*remap.+*@reuse:reuseaddress.+*@gpf_mask:GFPflagforallocatingvmemmappages.+*/+intvmemmap_remap_alloc(unsignedlongstart,unsignedlongend,+unsignedlongreuse,gfp_tgfp_mask)+{+LIST_HEAD(vmemmap_pages);+structvmemmap_remap_walkwalk={+.remap_pte=vmemmap_restore_pte,+.reuse_addr=reuse,+.vmemmap_pages=&vmemmap_pages,+};++/* See the comment in the vmemmap_remap_free(). */+BUG_ON(start-reuse!=PAGE_SIZE);++might_sleep_if(gfpflags_allow_blocking(gfp_mask));++if(alloc_vmemmap_page_list(start,end,gfp_mask,&vmemmap_pages))+return-ENOMEM;++vmemmap_remap_range(reuse,end,&walk);++return0;+}+/**Allocateablockofmemorytobeusedtobackthevirtualmemorymap*ortobackthepagetablesthatareusedtocreatethemapping.--
From: Muchun Song <hidden> Date: 2021-02-05 09:37:18
On Fri, Feb 5, 2021 at 4:59 PM Oscar Salvador [off-list ref] wrote:
On Thu, Feb 04, 2021 at 11:50:35AM +0800, Muchun Song wrote:
quoted
Changelog in v13 -> v14:
- Refuse to free the HugeTLB page when the system is under memory pressure.
- Use GFP_ATOMIC to allocate vmemmap pages instead of GFP_KERNEL.
- Rebase to linux-next 20210202.
- Fix and add some comments for vmemmap_remap_free().
Hi Oscar,
I reply to you in another thread (in the patch #4).
Thanks. :-)
quoted
Thanks to Oscar, Mike, David H and David R's suggestions and review.
Changelog in v12 -> v13:
- Remove VM_WARN_ON_PAGE macro.
- Add more comments in vmemmap_pte_range() and vmemmap_remap_free().
Thanks to Oscar and Mike's suggestions and review.
Changelog in v11 -> v12:
- Move VM_WARN_ON_PAGE to a separate patch.
- Call __free_hugepage() with hugetlb_lock (See patch #5.) to serialize
with dissolve_free_huge_page(). It is to prepare for patch #9.
- Introduce PageHugeInflight. See patch #9.
Changelog in v10 -> v11:
- Fix compiler error when !CONFIG_HUGETLB_PAGE_FREE_VMEMMAP.
- Rework some comments and commit changes.
- Rework vmemmap_remap_free() to 3 parameters.
Thanks to Oscar and Mike's suggestions and review.
Changelog in v9 -> v10:
- Fix a bug in patch #11. Thanks to Oscar for pointing that out.
- Rework some commit log or comments. Thanks Mike and Oscar for the suggestions.
- Drop VMEMMAP_TAIL_PAGE_REUSE in the patch #3.
Thank you very much Mike and Oscar for reviewing the code.
Changelog in v8 -> v9:
- Rework some code. Very thanks to Oscar.
- Put all the non-hugetlb vmemmap functions under sparsemem-vmemmap.c.
Changelog in v7 -> v8:
- Adjust the order of patches.
Very thanks to David and Oscar. Your suggestions are very valuable.
Changelog in v6 -> v7:
- Rebase to linux-next 20201130
- Do not use basepage mapping for vmemmap when this feature is disabled.
- Rework some patchs.
[PATCH v6 08/16] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page
[PATCH v6 10/16] mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb page
Thanks to Oscar and Barry.
Changelog in v5 -> v6:
- Disable PMD/huge page mapping of vmemmap if this feature was enabled.
- Simplify the first version code.
Changelog in v4 -> v5:
- Rework somme comments and code in the [PATCH v4 04/21] and [PATCH v4 05/21].
Thanks to Mike and Oscar's suggestions.
Changelog in v3 -> v4:
- Move all the vmemmap functions to hugetlb_vmemmap.c.
- Make the CONFIG_HUGETLB_PAGE_FREE_VMEMMAP default to y, if we want to
disable this feature, we should disable it by a boot/kernel command line.
- Remove vmemmap_pgtable_{init, deposit, withdraw}() helper functions.
- Initialize page table lock for vmemmap through core_initcall mechanism.
Thanks for Mike and Oscar's suggestions.
Changelog in v2 -> v3:
- Rename some helps function name. Thanks Mike.
- Rework some code. Thanks Mike and Oscar.
- Remap the tail vmemmap page with PAGE_KERNEL_RO instead of PAGE_KERNEL.
Thanks Matthew.
- Add some overhead analysis in the cover letter.
- Use vmemap pmd table lock instead of a hugetlb specific global lock.
Changelog in v1 -> v2:
- Fix do not call dissolve_compound_page in alloc_huge_page_vmemmap().
- Fix some typo and code style problems.
- Remove unused handle_vmemmap_fault().
- Merge some commits to one commit suggested by Mike.
Muchun Song (8):
mm: memory_hotplug: factor out bootmem core functions to
bootmem_info.c
mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP
mm: hugetlb: free the vmemmap pages associated with each HugeTLB page
mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap
mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate
mm: hugetlb: gather discrete indexes of tail page
mm: hugetlb: optimize the code with the help of the compiler
Documentation/admin-guide/kernel-parameters.txt | 14 ++
Documentation/admin-guide/mm/hugetlbpage.rst | 3 +
arch/x86/mm/init_64.c | 13 +-
fs/Kconfig | 6 +
include/linux/bootmem_info.h | 65 +++++
include/linux/hugetlb.h | 43 +++-
include/linux/hugetlb_cgroup.h | 19 +-
include/linux/memory_hotplug.h | 27 --
include/linux/mm.h | 5 +
mm/Makefile | 2 +
mm/bootmem_info.c | 124 ++++++++++
mm/hugetlb.c | 23 +-
mm/hugetlb_vmemmap.c | 314 ++++++++++++++++++++++++
mm/hugetlb_vmemmap.h | 33 +++
mm/memory_hotplug.c | 116 ---------
mm/sparse-vmemmap.c | 280 +++++++++++++++++++++
mm/sparse.c | 1 +
17 files changed, 930 insertions(+), 158 deletions(-)
create mode 100644 include/linux/bootmem_info.h
create mode 100644 mm/bootmem_info.c
create mode 100644 mm/hugetlb_vmemmap.c
create mode 100644 mm/hugetlb_vmemmap.h
--
2.11.0
From: Oscar Salvador <osalvador@suse.de> Date: 2021-02-05 11:56:51
On Thu, Feb 04, 2021 at 11:50:39AM +0800, Muchun Song wrote:
When we free a HugeTLB page to the buddy allocator, we should allocate the
vmemmap pages associated with it. But we may cannot allocate vmemmap pages
when the system is under memory pressure, in this case, we just refuse to
free the HugeTLB page instead of looping forever trying to allocate the
pages.
Signed-off-by: Muchun Song <redacted>
@@ -1397,16 +1397,26 @@ static void __free_huge_page(struct page *page)h->resv_huge_pages++;if(HPageTemporary(page)){-list_del(&page->lru);ClearHPageTemporary(page);++if(alloc_huge_page_vmemmap(h,page,GFP_ATOMIC)){+h->surplus_huge_pages++;+h->surplus_huge_pages_node[nid]++;+gotoenqueue;+}+list_del(&page->lru);update_and_free_page(h,page);}elseif(h->surplus_huge_pages_node[nid]){+if(alloc_huge_page_vmemmap(h,page,GFP_ATOMIC))+gotoenqueue;+/* remove the page from active list */list_del(&page->lru);update_and_free_page(h,page);h->surplus_huge_pages--;h->surplus_huge_pages_node[nid]--;}else{+enqueue:arch_clear_hugepage_flags(page);enqueue_huge_page(h,page);
Ok, we just keep them in the pool in case we fail to allocate.
+int alloc_huge_page_vmemmap(struct hstate *h, struct page *head, gfp_t gfp_mask)
+{
+ int ret;
+ unsigned long vmemmap_addr = (unsigned long)head;
+ unsigned long vmemmap_end, vmemmap_reuse;
+
+ if (!free_vmemmap_pages_per_hpage(h))
+ return 0;
+
+ vmemmap_addr += RESERVE_VMEMMAP_SIZE;
+ vmemmap_end = vmemmap_addr + free_vmemmap_pages_size_per_hpage(h);
+ vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
+
+ /*
+ * The pages which the vmemmap virtual address range [@vmemmap_addr,
+ * @vmemmap_end) are mapped to are freed to the buddy allocator, and
+ * the range is mapped to the page which @vmemmap_reuse is mapped to.
+ * When a HugeTLB page is freed to the buddy allocator, previously
+ * discarded vmemmap pages must be allocated and remapping.
+ */
+ ret = vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse,
+ gfp_mask | __GFP_NOWARN | __GFP_THISNODE);
Why don't you set all the GFP flags here?
vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse, GFP_ATOMIC|
__GFP_NOWARN | __GFP_THISNODE) ?
and replace this by while(--nr_pages) etc.
I did not really go in depth, but looks good to me, and much more simply
overall.
The only thing I am not sure about is the use of GFP_ATOMIC.
It has been raised before than when we are close to OOM, the user might want
to try to free up some memory by dissolving free_huge_pages, and so we might
want to dip in the reserves.
Given the fact that we are prepared to fail, and that we do not retry, I would
rather use GFP_KERNEL than to have X pages atomically allocated and then realize
we need to drop them on the ground because we cannot go further at some point.
I think those reserves would be better off used by someone else in that
situation.
But this is just my thoughs, and given the fact that there seems to be a consensus
of susing GFP_ATOMIC.
--
Oscar Salvador
SUSE L3
From: Muchun Song <hidden> Date: 2021-02-05 22:18:13
On Sat, Feb 6, 2021 at 12:01 AM Joao Martins [off-list ref] wrote:
On 2/4/21 3:50 AM, Muchun Song wrote:
quoted
Hi all,
[...]
quoted
When a HugeTLB is freed to the buddy system, we should allocate 6 pages for
vmemmap pages and restore the previous mapping relationship.
Apart from 2MB HugeTLB page, we also have 1GB HugeTLB page. It is similar
to the 2MB HugeTLB page. We also can use this approach to free the vmemmap
pages.
In this case, for the 1GB HugeTLB page, we can save 4094 pages. This is a
very substantial gain. On our server, run some SPDK/QEMU applications which
will use 1024GB hugetlbpage. With this feature enabled, we can save ~16GB
(1G hugepage)/~12GB (2MB hugepage) memory.
Because there are vmemmap page tables reconstruction on the freeing/allocating
path, it increases some overhead. Here are some overhead analysis.
[...]
quoted
Although the overhead has increased, the overhead is not significant. Like Mike
said, "However, remember that the majority of use cases create hugetlb pages at
or shortly after boot time and add them to the pool. So, additional overhead is
at pool creation time. There is no change to 'normal run time' operations of
getting a page from or returning a page to the pool (think page fault/unmap)".
Despite the overhead and in addition to the memory gains from this series ...
there's an additional benefit there isn't talked here with your vmemmap page
reuse trick. That is page (un)pinners will see an improvement and I presume because
there are fewer memmap pages and thus the tail/head pages are staying in cache more
often.
Out of the box I saw (when comparing linux-next against linux-next + this series)
with gup_test and pinning a 16G hugetlb file (with 1G pages):
get_user_pages(): ~32k -> ~9k
unpin_user_pages(): ~75k -> ~70k
Usually any tight loop fetching compound_head(), or reading tail pages data (e.g.
compound_head) benefit a lot. There's some unpinning inefficiencies I am fixing[0], but
with that in added it shows even more:
unpin_user_pages(): ~27k -> ~3.8k
FWIW, I was also seeing that with devdax and the ZONE_DEVICE vmemmap page reuse equivalent
series[1] but it was mixed with other numbers.
It's really a surprise. Thank you very much for the test data.
Very nice. Thanks again.
When a HugeTLB is freed to the buddy system, we should allocate 6 pages for
vmemmap pages and restore the previous mapping relationship.
Apart from 2MB HugeTLB page, we also have 1GB HugeTLB page. It is similar
to the 2MB HugeTLB page. We also can use this approach to free the vmemmap
pages.
In this case, for the 1GB HugeTLB page, we can save 4094 pages. This is a
very substantial gain. On our server, run some SPDK/QEMU applications which
will use 1024GB hugetlbpage. With this feature enabled, we can save ~16GB
(1G hugepage)/~12GB (2MB hugepage) memory.
Because there are vmemmap page tables reconstruction on the freeing/allocating
path, it increases some overhead. Here are some overhead analysis.
[...]
Although the overhead has increased, the overhead is not significant. Like Mike
said, "However, remember that the majority of use cases create hugetlb pages at
or shortly after boot time and add them to the pool. So, additional overhead is
at pool creation time. There is no change to 'normal run time' operations of
getting a page from or returning a page to the pool (think page fault/unmap)".
Despite the overhead and in addition to the memory gains from this series ...
there's an additional benefit there isn't talked here with your vmemmap page
reuse trick. That is page (un)pinners will see an improvement and I presume because
there are fewer memmap pages and thus the tail/head pages are staying in cache more
often.
Out of the box I saw (when comparing linux-next against linux-next + this series)
with gup_test and pinning a 16G hugetlb file (with 1G pages):
get_user_pages(): ~32k -> ~9k
unpin_user_pages(): ~75k -> ~70k
Usually any tight loop fetching compound_head(), or reading tail pages data (e.g.
compound_head) benefit a lot. There's some unpinning inefficiencies I am fixing[0], but
with that in added it shows even more:
unpin_user_pages(): ~27k -> ~3.8k
FWIW, I was also seeing that with devdax and the ZONE_DEVICE vmemmap page reuse equivalent
series[1] but it was mixed with other numbers.
Anyways, JFYI :)
Joao
[0] https://lore.kernel.org/linux-mm/20210204202500.26474-1-joao.m.martins@oracle.com/
[1] https://lore.kernel.org/linux-mm/20201208172901.17384-1-joao.m.martins@oracle.com/
From: Muchun Song <hidden> Date: 2021-02-05 22:26:32
On Fri, Feb 5, 2021 at 4:54 PM Oscar Salvador [off-list ref] wrote:
On Thu, Feb 04, 2021 at 11:50:38AM +0800, Muchun Song wrote:
quoted
Every HugeTLB has more than one struct page structure. We __know__ that
we only use the first 4(HUGETLB_CGROUP_MIN_ORDER) struct page structures
to store metadata associated with each HugeTLB.
There are a lot of struct page structures associated with each HugeTLB
page. For tail pages, the value of compound_head is the same. So we can
reuse first page of tail page structures. We map the virtual addresses
of the remaining pages of tail page structures to the first tail page
struct, and then free these page frames. Therefore, we need to reserve
two pages as vmemmap areas.
When we allocate a HugeTLB page from the buddy, we can free some vmemmap
pages associated with each HugeTLB page. It is more appropriate to do it
in the prep_new_huge_page().
The free_vmemmap_pages_per_hpage(), which indicates how many vmemmap
pages associated with a HugeTLB page can be freed, returns zero for
now, which means the feature is disabled. We will enable it once all
the infrastructure is there.
Signed-off-by: Muchun Song <redacted>
---
[...]
quoted
+void free_huge_page_vmemmap(struct hstate *h, struct page *head)
+{
+ unsigned long vmemmap_addr = (unsigned long)head;
+ unsigned long vmemmap_end, vmemmap_reuse;
+
+ if (!free_vmemmap_pages_per_hpage(h))
+ return;
+
+ vmemmap_addr += RESERVE_VMEMMAP_SIZE;
+ vmemmap_end = vmemmap_addr + free_vmemmap_pages_size_per_hpage(h);
+ vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
+
+ /*
+ * Remap the vmemmap virtual address range [@vmemmap_addr, @vmemmap_end)
+ * to the page which @vmemmap_reuse is mapped to, then free the vmemmap
+ * pages which the range are mapped to.
"then free the pages which the range [@vmemmap_addr, @vmemmap_end] is mapped to."
I am not a native but sounds better to me.
Well, we BUG_ON on empty PTE, so not sure that pointing out here is worth.
It sounds like we do nothing when it's empty.
Maybe:
"called for each lowest-level entry (PTE)"
Thanks. I will update this.
quoted
+ * @reuse_page: the page which is reused for the tail vmemmap pages.
+ * @reuse_addr: the virtual address of the @reuse_page page.
+ * @vmemmap_pages: the list head of the vmemmap pages that can be freed.
+ */
+struct vmemmap_remap_walk {
+ void (*remap_pte)(pte_t *pte, unsigned long addr,
+ struct vmemmap_remap_walk *walk);
+ struct page *reuse_page;
+ unsigned long reuse_addr;
+ struct list_head *vmemmap_pages;
+};
+
+static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
+ unsigned long end,
+ struct vmemmap_remap_walk *walk)
+{
+ pte_t *pte;
+
+ pte = pte_offset_kernel(pmd, addr);
+
+ /*
+ * The reuse_page is found 'first' in table walk before we start
+ * remapping (which is calling @walk->remap_pte).
+ */
+ if (!walk->reuse_page) {
+ BUG_ON(pte_none(*pte) || walk->reuse_addr != addr);
I would rather have them in separate lines:
BUG_ON(pte_none(*pte));
BUG_ON(walk->reuse_addr != addr));
It helps when trying to figure out when we explode. One could dig in the
registers, but let's make it easier to find out.
OK. Will do.
quoted
+
[...]
quoted
+static void vmemmap_remap_range(unsigned long start, unsigned long end,
+ struct vmemmap_remap_walk *walk)
+{
+ unsigned long addr = start;
+ unsigned long next;
+ pgd_t *pgd;
+
+ VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE));
+ VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE));
+
+ pgd = pgd_offset_k(addr);
+ do {
+ BUG_ON(pgd_none(*pgd));
+
+ next = pgd_addr_end(addr, end);
+ vmemmap_p4d_range(pgd, addr, next, walk);
+ } while (pgd++, addr = next, addr != end);
+
+ /*
+ * We do not change the mapping of the vmemmap virtual address range
+ * [@start, @start + PAGE_SIZE) which belongs to the reuse range.
+ * So we not need to flush the TLB.
+ */
+ flush_tlb_kernel_range(start + PAGE_SIZE, end);
I find that comment a bit confusing. I would rather describe what are we
flushing instead of what we are not.
OK. Will update it.
quoted
+}
+
+/*
+ * Free a vmemmap page. A vmemmap page can be allocated from the memblock
+ * allocator or buddy allocator. If the PG_reserved flag is set, it means
+ * that it allocated from the memblock allocator, just free it via the
+ * free_bootmem_page(). Otherwise, use __free_page().
+ */
+static inline void free_vmemmap_page(struct page *page)
+{
+ if (PageReserved(page))
+ free_bootmem_page(page);
+ else
+ __free_page(page);
+}
+
+/* Free a list of the vmemmap pages */
+static void free_vmemmap_page_list(struct list_head *list)
+{
+ struct page *page, *next;
+
+ list_for_each_entry_safe(page, next, list, lru) {
+ list_del(&page->lru);
+ free_vmemmap_page(page);
+ }
+}
+
+static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
+ struct vmemmap_remap_walk *walk)
+{
+ /*
+ * Remap the tail pages as read-only to catch illegal write operation
+ * to the tail pages.
+ */
+ pgprot_t pgprot = PAGE_KERNEL_RO;
+ pte_t entry = mk_pte(walk->reuse_page, pgprot);
+ struct page *page = pte_page(*pte);
+
+ list_add(&page->lru, walk->vmemmap_pages);
+ set_pte_at(&init_mm, addr, pte, entry);
+}
+
+/**
+ * vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
+ * to the page which @reuse is mapped to, then free vmemmap
+ * which the range are mapped to.
+ * @start: start address of the vmemmap virtual address range that we want
+ * to remap.
+ * @end: end address of the vmemmap virtual address range that we want to
+ * remap.
+ * @reuse: reuse address.
+ *
+ * Note: This function depends on vmemmap being base page mapped. Please make
+ * sure that the architecture disables PMD mapping of vmemmap pages when calling
+ * this function.
Well, we do not really depend on the architecture to not map the vmemmap range
with PMDs, right? IIUC, that is driven by your boot parameter (patch#5), which
overrides whatever the architecture can do.
Right. I will rework the comment here.
Functional changes look good to me, so with all the above fixes, you can add:
Reviewed-by: Oscar Salvador <osalvador@suse.de>
From: Muchun Song <hidden> Date: 2021-02-06 08:03:34
On Fri, Feb 5, 2021 at 7:54 PM Oscar Salvador [off-list ref] wrote:
On Thu, Feb 04, 2021 at 11:50:39AM +0800, Muchun Song wrote:
quoted
When we free a HugeTLB page to the buddy allocator, we should allocate the
vmemmap pages associated with it. But we may cannot allocate vmemmap pages
when the system is under memory pressure, in this case, we just refuse to
free the HugeTLB page instead of looping forever trying to allocate the
pages.
Signed-off-by: Muchun Song <redacted>
@@ -1397,16 +1397,26 @@ static void __free_huge_page(struct page *page)h->resv_huge_pages++;if(HPageTemporary(page)){-list_del(&page->lru);ClearHPageTemporary(page);++if(alloc_huge_page_vmemmap(h,page,GFP_ATOMIC)){+h->surplus_huge_pages++;+h->surplus_huge_pages_node[nid]++;+gotoenqueue;+}+list_del(&page->lru);update_and_free_page(h,page);}elseif(h->surplus_huge_pages_node[nid]){+if(alloc_huge_page_vmemmap(h,page,GFP_ATOMIC))+gotoenqueue;+/* remove the page from active list */list_del(&page->lru);update_and_free_page(h,page);h->surplus_huge_pages--;h->surplus_huge_pages_node[nid]--;}else{+enqueue:arch_clear_hugepage_flags(page);enqueue_huge_page(h,page);
Ok, we just keep them in the pool in case we fail to allocate.
+int alloc_huge_page_vmemmap(struct hstate *h, struct page *head, gfp_t gfp_mask)
+{
+ int ret;
+ unsigned long vmemmap_addr = (unsigned long)head;
+ unsigned long vmemmap_end, vmemmap_reuse;
+
+ if (!free_vmemmap_pages_per_hpage(h))
+ return 0;
+
+ vmemmap_addr += RESERVE_VMEMMAP_SIZE;
+ vmemmap_end = vmemmap_addr + free_vmemmap_pages_size_per_hpage(h);
+ vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
+
+ /*
+ * The pages which the vmemmap virtual address range [@vmemmap_addr,
+ * @vmemmap_end) are mapped to are freed to the buddy allocator, and
+ * the range is mapped to the page which @vmemmap_reuse is mapped to.
+ * When a HugeTLB page is freed to the buddy allocator, previously
+ * discarded vmemmap pages must be allocated and remapping.
+ */
+ ret = vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse,
+ gfp_mask | __GFP_NOWARN | __GFP_THISNODE);
Why don't you set all the GFP flags here?
Originally, I wanted to let the caller know the GFP flag which they
used. But setting all the GFP flags here also makes sense to me.
And we can remove the @gfp_mask parameter of the
alloc_huge_page_vmemmap. It is simple.
I did not really go in depth, but looks good to me, and much more simply
overall.
Yeah. The series only has 8 patches now. It is simpler.
The only thing I am not sure about is the use of GFP_ATOMIC.
It has been raised before than when we are close to OOM, the user might want
to try to free up some memory by dissolving free_huge_pages, and so we might
want to dip in the reserves.
Given the fact that we are prepared to fail, and that we do not retry, I would
rather use GFP_KERNEL than to have X pages atomically allocated and then realize
we need to drop them on the ground because we cannot go further at some point.
I think those reserves would be better off used by someone else in that
situation.
But this is just my thoughs, and given the fact that there seems to be a consensus
of susing GFP_ATOMIC.
--
Oscar Salvador
SUSE L3