On Mon, 2021-06-07 at 15:10 +1000, David Gibson wrote:

On Fri, Apr 30, 2021 at 11:36:08AM -0300, Leonardo Bras wrote:

quoted

Every time a memory hotplug happens, and the memory limit crosses a
2^n
value, it may be necessary to perform HPT resizing-up, which can
take
some time (over 100ms in my tests).

It usually is not an issue, but it can take some time if a lot of
memory
is added to a guest with little starting memory:
Adding 256G to a 2GB guest, for example will require 8 HPT resizes.

Perform an HPT resize before memory hotplug, updating HPT to its
final size (considering a successful hotplug), taking the number of
HPT resizes to at most one per memory hotplug action.

Signed-off-by: Leonardo Bras <redacted>

Reviewed-by: David Gibson <redacted>

Thanks David!

quoted

---
 arch/powerpc/include/asm/book3s/64/hash.h     |  2 ++
 arch/powerpc/mm/book3s64/hash_utils.c         | 20
+++++++++++++++++++
 .../platforms/pseries/hotplug-memory.c        |  9 +++++++++
 3 files changed, 31 insertions(+)

diff --git a/arch/powerpc/include/asm/book3s/64/hash.h

b/arch/powerpc/include/asm/book3s/64/hash.h
index d959b0195ad9..fad4af8b8543 100644

--- a/arch/powerpc/include/asm/book3s/64/hash.h
+++ b/arch/powerpc/include/asm/book3s/64/hash.h

@@ -255,6 +255,8 @@ int hash__create_section_mapping(unsigned long

start, unsigned long end,
                                 int nid, pgprot_t prot);
 int hash__remove_section_mapping(unsigned long start, unsigned
long end);
 
+void hash_batch_expand_prepare(unsigned long newsize);
+
 #endif /* !__ASSEMBLY__ */
 #endif /* __KERNEL__ */
 #endif /* _ASM_POWERPC_BOOK3S_64_HASH_H */

diff --git a/arch/powerpc/mm/book3s64/hash_utils.c

b/arch/powerpc/mm/book3s64/hash_utils.c
index 608e4ed397a9..3fa395b3fe57 100644

--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c

@@ -859,6 +859,26 @@ int hash__remove_section_mapping(unsigned long

start, unsigned long end)
 
        return rc;
 }
+
+void hash_batch_expand_prepare(unsigned long newsize)
+{
+       const u64 starting_size = ppc64_pft_size;
+
+       /*
+        * Resizing-up HPT should never fail, but there are some
cases system starts with higher
+        * SHIFT than required, and we go through the funny case of
resizing HPT down while
+        * adding memory
+        */
+
+       while (resize_hpt_for_hotplug(newsize, false) == -ENOSPC) {
+               newsize *= 2;
+               pr_warn("Hash collision while resizing HPT\n");
+
+               /* Do not try to resize to the starting size, or
bigger value */
+               if (htab_shift_for_mem_size(newsize) >=
starting_size)
+                       break;
+       }
+}
 #endif /* CONFIG_MEMORY_HOTPLUG */
 
 static void __init hash_init_partition_table(phys_addr_t
hash_table,

diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c

b/arch/powerpc/platforms/pseries/hotplug-memory.c
index 8377f1f7c78e..48b2cfe4ce69 100644

--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c

@@ -13,6 +13,7 @@

 #include <linux/memory.h>
 #include <linux/memory_hotplug.h>
 #include <linux/slab.h>
+#include <linux/pgtable.h>
 
 #include <asm/firmware.h>
 #include <asm/machdep.h>

@@ -671,6 +672,10 @@ static int dlpar_memory_add_by_count(u32

lmbs_to_add)
        if (lmbs_available < lmbs_to_add)
                return -EINVAL;
 
+       if (!radix_enabled())
+               hash_batch_expand_prepare(memblock_phys_mem_size()
+
+                                                lmbs_to_add *
drmem_lmb_size());
+
        for_each_drmem_lmb(lmb) {
                if (lmb->flags & DRCONF_MEM_ASSIGNED)
                        continue;

@@ -788,6 +793,10 @@ static int dlpar_memory_add_by_ic(u32

lmbs_to_add, u32 drc_index)
        if (lmbs_available < lmbs_to_add)
                return -EINVAL;
 
+       if (!radix_enabled())
+               hash_batch_expand_prepare(memblock_phys_mem_size()
+
+                                         lmbs_to_add *
drmem_lmb_size());
+
        for_each_drmem_lmb_in_range(lmb, start_lmb, end_lmb) {
                if (lmb->flags & DRCONF_MEM_ASSIGNED)
                        continue;

-- 
David Gibson                    | I'll have my music baroque, and my
code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_
_other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson