The patch titled
Subject: mm: swap: reuse exclusive folio directly instead of wp page faults
has been added to the -mm mm-unstable branch. Its filename is
mm-swap-reuse-exclusive-folio-directly-instead-of-wp-page-faults.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap-reuse-exclusive-folio-directly-instead-of-wp-page-faults.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Barry Song <v-songbaohua@xxxxxxxx>
Subject: mm: swap: reuse exclusive folio directly instead of wp page faults
Date: Sun, 2 Jun 2024 12:45:02 +1200
After swapping out, we perform a swap-in operation. If we first read and
then write, we encounter a major fault in do_swap_page for reading, along
with additional minor faults in do_wp_page for writing. However, the
latter appears to be unnecessary and inefficient. Instead, we can
directly reuse in do_swap_page and completely eliminate the need for
do_wp_page.
This patch achieves that optimization specifically for exclusive folios.
The following microbenchmark demonstrates the significant reduction in
minor faults.
#define DATA_SIZE (2UL * 1024 * 1024)
#define PAGE_SIZE (4UL * 1024)
static void *read_write_data(char *addr)
{
char tmp;
for (int i = 0; i < DATA_SIZE; i += PAGE_SIZE) {
tmp = *(volatile char *)(addr + i);
*(volatile char *)(addr + i) = tmp;
}
}
int main(int argc, char **argv)
{
struct rusage ru;
char *addr = mmap(NULL, DATA_SIZE, PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
memset(addr, 0x11, DATA_SIZE);
do {
long old_ru_minflt, old_ru_majflt;
long new_ru_minflt, new_ru_majflt;
madvise(addr, DATA_SIZE, MADV_PAGEOUT);
getrusage(RUSAGE_SELF, &ru);
old_ru_minflt = ru.ru_minflt;
old_ru_majflt = ru.ru_majflt;
read_write_data(addr);
getrusage(RUSAGE_SELF, &ru);
new_ru_minflt = ru.ru_minflt;
new_ru_majflt = ru.ru_majflt;
printf("minor faults:%ld major faults:%ld\n",
new_ru_minflt - old_ru_minflt,
new_ru_majflt - old_ru_majflt);
} while(0);
return 0;
}
w/o patch,
/ # ~/a.out
minor faults:512 major faults:512
w/ patch,
/ # ~/a.out
minor faults:0 major faults:512
Minor faults decrease to 0!
Link: https://lkml.kernel.org/r/20240602004502.26895-1-21cnbao@xxxxxxxxx
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Chris Li <chrisl@xxxxxxxxxx>
Cc: Kairui Song <kasong@xxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)
--- a/mm/memory.c~mm-swap-reuse-exclusive-folio-directly-instead-of-wp-page-faults
+++ a/mm/memory.c
@@ -4308,6 +4308,10 @@ check_folio:
add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages);
add_mm_counter(vma->vm_mm, MM_SWAPENTS, -nr_pages);
pte = mk_pte(page, vma->vm_page_prot);
+ if (pte_swp_soft_dirty(vmf->orig_pte))
+ pte = pte_mksoft_dirty(pte);
+ if (pte_swp_uffd_wp(vmf->orig_pte))
+ pte = pte_mkuffd_wp(pte);
/*
* Same logic as in do_wp_page(); however, optimize for pages that are
@@ -4317,18 +4321,18 @@ check_folio:
*/
if (!folio_test_ksm(folio) &&
(exclusive || folio_ref_count(folio) == 1)) {
- if (vmf->flags & FAULT_FLAG_WRITE) {
- pte = maybe_mkwrite(pte_mkdirty(pte), vma);
- vmf->flags &= ~FAULT_FLAG_WRITE;
+ if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) &&
+ !vma_soft_dirty_enabled(vma)) {
+ pte = pte_mkwrite(pte, vma);
+ if (vmf->flags & FAULT_FLAG_WRITE) {
+ pte = pte_mkdirty(pte);
+ vmf->flags &= ~FAULT_FLAG_WRITE;
+ }
}
rmap_flags |= RMAP_EXCLUSIVE;
}
folio_ref_add(folio, nr_pages - 1);
flush_icache_pages(vma, page, nr_pages);
- if (pte_swp_soft_dirty(vmf->orig_pte))
- pte = pte_mksoft_dirty(pte);
- if (pte_swp_uffd_wp(vmf->orig_pte))
- pte = pte_mkuffd_wp(pte);
vmf->orig_pte = pte_advance_pfn(pte, page_idx);
/* ksm created a completely new copy */
_
Patches currently in -mm which might be from v-songbaohua@xxxxxxxx are
mm-huge_mm-fix-undefined-reference-to-mthp_stats-for-config_sysfs=n.patch
mm-arm64-fix-the-out-of-bounds-issue-in-contpte_clear_young_dirty_ptes.patch
mm-remove-the-implementation-of-swap_free-and-always-use-swap_free_nr.patch
mm-introduce-pte_move_swp_offset-helper-which-can-move-offset-bidirectionally.patch
mm-introduce-arch_do_swap_page_nr-which-allows-restore-metadata-for-nr-pages.patch
mm-swap-reuse-exclusive-folio-directly-instead-of-wp-page-faults.patch
