On Wed, Jul 17, 2019 at 03:14:57PM -0700, Suren Baghdasaryan wrote:

Hi Minchan,
Couple comments inline.
Thanks!

On Sun, Jul 14, 2019 at 4:34 PM Minchan Kim [off-list ref] wrote:

quoted

When a process expects no accesses to a certain memory range, it could
give a hint to kernel that the pages can be reclaimed when memory pressure
happens but data should be preserved for future use.  This could reduce
workingset eviction so it ends up increasing performance.

This patch introduces the new MADV_COLD hint to madvise(2) syscall.
MADV_COLD can be used by a process to mark a memory range as not expected
to be used in the near future. The hint can help kernel in deciding which
pages to evict early during memory pressure.

It works for every LRU pages like MADV_[DONTNEED|FREE]. IOW, It moves

        active file page -> inactive file LRU
        active anon page -> inacdtive anon LRU

Unlike MADV_FREE, it doesn't move active anonymous pages to inactive
file LRU's head because MADV_COLD is a little bit different symantic.
MADV_FREE means it's okay to discard when the memory pressure because
the content of the page is *garbage* so freeing such pages is almost zero
overhead since we don't need to swap out and access afterward causes just
minor fault. Thus, it would make sense to put those freeable pages in
inactive file LRU to compete other used-once pages. It makes sense for
implmentaion point of view, too because it's not swapbacked memory any
longer until it would be re-dirtied. Even, it could give a bonus to make
them be reclaimed on swapless system. However, MADV_COLD doesn't mean
garbage so reclaiming them requires swap-out/in in the end so it's bigger
cost. Since we have designed VM LRU aging based on cost-model, anonymous
cold pages would be better to position inactive anon's LRU list, not file
LRU. Furthermore, it would help to avoid unnecessary scanning if system
doesn't have a swap device. Let's start simpler way without adding
complexity at this moment. However, keep in mind, too that it's a caveat
that workloads with a lot of pages cache are likely to ignore MADV_COLD
on anonymous memory because we rarely age anonymous LRU lists.

* man-page material

MADV_COLD (since Linux x.x)

Pages in the specified regions will be treated as less-recently-accessed
compared to pages in the system with similar access frequencies.
In contrast to MADV_FREE, the contents of the region are preserved
regardless of subsequent writes to pages.

MADV_COLD cannot be applied to locked pages, Huge TLB pages, or VM_PFNMAP
pages.

* v2
 * add up the warn with lots of page cache workload - mhocko
 * add man page stuff - dave

* v1
 * remove page_mapcount filter - hannes, mhocko
 * remove idle page handling - joelaf

* RFCv2
 * add more description - mhocko

* RFCv1
 * renaming from MADV_COOL to MADV_COLD - hannes

* internal review
 * use clear_page_youn in deactivate_page - joelaf
 * Revise the description - surenb
 * Renaming from MADV_WARM to MADV_COOL - surenb

Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 include/linux/swap.h                   |   1 +
 include/uapi/asm-generic/mman-common.h |   1 +
 mm/internal.h                          |   2 +-
 mm/madvise.c                           | 180 ++++++++++++++++++++++++-
 mm/oom_kill.c                          |   2 +-
 mm/swap.c                              |  42 ++++++
 6 files changed, 224 insertions(+), 4 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index de2c67a33b7e..0ce997edb8bb 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h

@@ -340,6 +340,7 @@ extern void lru_add_drain_cpu(int cpu);
 extern void lru_add_drain_all(void);
 extern void rotate_reclaimable_page(struct page *page);
 extern void deactivate_file_page(struct page *page);
+extern void deactivate_page(struct page *page);
 extern void mark_page_lazyfree(struct page *page);
 extern void swap_setup(void);

diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index 63b1f506ea67..ef8a56927b12 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h

@@ -45,6 +45,7 @@
 #define MADV_SEQUENTIAL        2               /* expect sequential page references */
 #define MADV_WILLNEED  3               /* will need these pages */
 #define MADV_DONTNEED  4               /* don't need these pages */
+#define MADV_COLD      5               /* deactivatie these pages */

s/deactivatie/deactivate

Fixed.

quoted

 /* common parameters: try to keep these consistent across architectures */
 #define MADV_FREE      8               /* free pages only if memory pressure */

diff --git a/mm/internal.h b/mm/internal.h
index f53a14d67538..c61b215ff265 100644
--- a/mm/internal.h
+++ b/mm/internal.h

@@ -39,7 +39,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf);
 void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
                unsigned long floor, unsigned long ceiling);

-static inline bool can_madv_dontneed_vma(struct vm_area_struct *vma)
+static inline bool can_madv_lru_vma(struct vm_area_struct *vma)
 {
        return !(vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP));
 }

diff --git a/mm/madvise.c b/mm/madvise.c
index 968df3aa069f..bae0055f9724 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c

@@ -40,6 +40,7 @@ static int madvise_need_mmap_write(int behavior)
        case MADV_REMOVE:
        case MADV_WILLNEED:
        case MADV_DONTNEED:
+       case MADV_COLD:
        case MADV_FREE:
                return 0;
        default:

@@ -307,6 +308,178 @@ static long madvise_willneed(struct vm_area_struct *vma,
        return 0;
 }

+static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr,
+                               unsigned long end, struct mm_walk *walk)
+{
+       struct mmu_gather *tlb = walk->private;
+       struct mm_struct *mm = tlb->mm;
+       struct vm_area_struct *vma = walk->vma;
+       pte_t *orig_pte, *pte, ptent;
+       spinlock_t *ptl;
+       struct page *page;
+       unsigned long next;
+
+       next = pmd_addr_end(addr, end);
+       if (pmd_trans_huge(*pmd)) {
+               pmd_t orig_pmd;
+
+               tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
+               ptl = pmd_trans_huge_lock(pmd, vma);
+               if (!ptl)
+                       return 0;
+
+               orig_pmd = *pmd;
+               if (is_huge_zero_pmd(orig_pmd))
+                       goto huge_unlock;
+
+               if (unlikely(!pmd_present(orig_pmd))) {
+                       VM_BUG_ON(thp_migration_supported() &&
+                                       !is_pmd_migration_entry(orig_pmd));
+                       goto huge_unlock;
+               }
+
+               page = pmd_page(orig_pmd);
+               if (next - addr != HPAGE_PMD_SIZE) {
+                       int err;
+
+                       if (page_mapcount(page) != 1)
+                               goto huge_unlock;
+
+                       get_page(page);
+                       spin_unlock(ptl);
+                       lock_page(page);
+                       err = split_huge_page(page);
+                       unlock_page(page);
+                       put_page(page);
+                       if (!err)
+                               goto regular_page;
+                       return 0;
+               }
+
+               if (pmd_young(orig_pmd)) {
+                       pmdp_invalidate(vma, addr, pmd);
+                       orig_pmd = pmd_mkold(orig_pmd);
+
+                       set_pmd_at(mm, addr, pmd, orig_pmd);
+                       tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
+               }
+
+               test_and_clear_page_young(page);
+               deactivate_page(page);
+huge_unlock:
+               spin_unlock(ptl);
+               return 0;
+       }
+
+       if (pmd_trans_unstable(pmd))
+               return 0;
+
+regular_page:
+       tlb_change_page_size(tlb, PAGE_SIZE);
+       orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+       flush_tlb_batched_pending(mm);
+       arch_enter_lazy_mmu_mode();
+       for (; addr < end; pte++, addr += PAGE_SIZE) {
+               ptent = *pte;
+
+               if (pte_none(ptent))
+                       continue;
+
+               if (!pte_present(ptent))
+                       continue;
+
+               page = vm_normal_page(vma, addr, ptent);
+               if (!page)
+                       continue;
+
+               /*
+                * Creating a THP page is expensive so split it only if we
+                * are sure it's worth. Split it if we are only owner.
+                */
+               if (PageTransCompound(page)) {
+                       if (page_mapcount(page) != 1)
+                               break;
+                       get_page(page);
+                       if (!trylock_page(page)) {
+                               put_page(page);
+                               break;
+                       }
+                       pte_unmap_unlock(orig_pte, ptl);
+                       if (split_huge_page(page)) {
+                               unlock_page(page);
+                               put_page(page);
+                               pte_offset_map_lock(mm, pmd, addr, &ptl);
+                               break;
+                       }
+                       unlock_page(page);
+                       put_page(page);
+                       pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+                       pte--;
+                       addr -= PAGE_SIZE;
+                       continue;
+               }
+
+               VM_BUG_ON_PAGE(PageTransCompound(page), page);
+
+               if (pte_young(ptent)) {
+                       ptent = ptep_get_and_clear_full(mm, addr, pte,
+                                                       tlb->fullmm);
+                       ptent = pte_mkold(ptent);
+                       set_pte_at(mm, addr, pte, ptent);
+                       tlb_remove_tlb_entry(tlb, pte, addr);
+               }
+
+               /*
+                * We are deactivating a page for accelerating reclaiming.
+                * VM couldn't reclaim the page unless we clear PG_young.
+                * As a side effect, it makes confuse idle-page tracking
+                * because they will miss recent referenced history.
+                */
+               test_and_clear_page_young(page);
+               deactivate_page(page);
+       }
+
+       arch_enter_lazy_mmu_mode();

Did you mean to say arch_leave_lazy_mmu_mode() ?

Oops, Fixed.

Thanks, Suren!