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authorPeter Xu <peterx@redhat.com>2022-08-11 12:13:29 -0400
committerAndrew Morton <akpm@linux-foundation.org>2022-09-26 19:46:05 -0700
commit2e3468778dbe3ec389a10c21a703bb8e5be5cfbc (patch)
tree7b42c090cd95bdd97a45ab207c9453da71b2d25c /mm/rmap.c
parent0ccf7f168e17bb7eb5a322397ba5a841f4fbaccb (diff)
mm: remember young/dirty bit for page migrations
When page migration happens, we always ignore the young/dirty bit settings in the old pgtable, and marking the page as old in the new page table using either pte_mkold() or pmd_mkold(), and keeping the pte clean. That's fine from functional-wise, but that's not friendly to page reclaim because the moving page can be actively accessed within the procedure. Not to mention hardware setting the young bit can bring quite some overhead on some systems, e.g. x86_64 needs a few hundreds nanoseconds to set the bit. The same slowdown problem to dirty bits when the memory is first written after page migration happened. Actually we can easily remember the A/D bit configuration and recover the information after the page is migrated. To achieve it, define a new set of bits in the migration swap offset field to cache the A/D bits for old pte. Then when removing/recovering the migration entry, we can recover the A/D bits even if the page changed. One thing to mention is that here we used max_swapfile_size() to detect how many swp offset bits we have, and we'll only enable this feature if we know the swp offset is big enough to store both the PFN value and the A/D bits. Otherwise the A/D bits are dropped like before. Link: https://lkml.kernel.org/r/20220811161331.37055-6-peterx@redhat.com Signed-off-by: Peter Xu <peterx@redhat.com> Reviewed-by: "Huang, Ying" <ying.huang@intel.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Andi Kleen <andi.kleen@intel.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: "Kirill A . Shutemov" <kirill@shutemov.name> Cc: Minchan Kim <minchan@kernel.org> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Dave Hansen <dave.hansen@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/rmap.c')
-rw-r--r--mm/rmap.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/mm/rmap.c b/mm/rmap.c
index 6781f693df50..131def40e4f0 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2066,7 +2066,10 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
else
entry = make_readable_migration_entry(
page_to_pfn(subpage));
-
+ if (pte_young(pteval))
+ entry = make_migration_entry_young(entry);
+ if (pte_dirty(pteval))
+ entry = make_migration_entry_dirty(entry);
swp_pte = swp_entry_to_pte(entry);
if (pte_soft_dirty(pteval))
swp_pte = pte_swp_mksoft_dirty(swp_pte);