The patch titled
Subject: mm/ksm: remove page_mapcount() usage in stable_tree_search()
has been added to the -mm mm-unstable branch. Its filename is
mm-ksm-remove-page_mapcount-usage-in-stable_tree_search.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-ksm-remove-page_mapcount-usage-in-stable_tree_search.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: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/ksm: remove page_mapcount() usage in stable_tree_search()
Date: Tue, 16 Apr 2024 19:25:33 +0200
We want to limit the use of page_mapcount() to the places where it is
absolutely necessary.
If our folio has a stable node, it is a (small) KSM folio -- see
folio_stable_node(). Let's use folio_mapcount() in stable_tree_search()
instead, which results in no functional change.
The mapcount > 1 check is a bit confusing, because that's usually a check
for page sharing. Looks like the reason is that we are guaranteed to not
exceed ksm_max_page_sharing for the tree KSM folio when merging with that.
Let's update the documentation to make that clearer.
Link: https://lkml.kernel.org/r/20240416172533.663418-1-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Alex Shi (tencent) <alexs@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/ksm.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
--- a/mm/ksm.c~mm-ksm-remove-page_mapcount-usage-in-stable_tree_search
+++ a/mm/ksm.c
@@ -1909,12 +1909,15 @@ again:
if (page_node) {
VM_BUG_ON(page_node->head != &migrate_nodes);
/*
- * Test if the migrated page should be merged
- * into a stable node dup. If the mapcount is
- * 1 we can migrate it with another KSM page
- * without adding it to the chain.
+ * If the mapcount of our migrated KSM folio is
+ * at most 1, we can merge it with another
+ * KSM folio where we know that we have space
+ * for one more mapping without exceeding the
+ * ksm_max_page_sharing limit: see
+ * chain_prune(). This way, we can avoid adding
+ * this stable node to the chain.
*/
- if (page_mapcount(page) > 1)
+ if (folio_mapcount(folio) > 1)
goto chain_append;
}
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-madvise-make-madv_populate_readwrite-handle-vm_fault_retry-properly.patch
mm-madvise-dont-perform-madvise-vma-walk-for-madv_populate_readwrite.patch
mm-convert-folio_estimated_sharers-to-folio_likely_mapped_shared.patch
mm-convert-folio_estimated_sharers-to-folio_likely_mapped_shared-fix.patch
selftests-memfd_secret-add-vmsplice-test.patch
mm-merge-folio_is_secretmem-and-folio_fast_pin_allowed-into-gup_fast_folio_allowed.patch
mm-optimize-config_per_vma_lock-member-placement-in-vm_area_struct.patch
mm-remove-prot-parameter-from-move_pte.patch
mm-gup-consistently-name-gup-fast-functions.patch
mm-treewide-rename-config_have_fast_gup-to-config_have_gup_fast.patch
mm-use-gup-fast-instead-fast-gup-in-remaining-comments.patch
drivers-virt-acrn-fix-pfnmap-pte-checks-in-acrn_vm_ram_map.patch
mm-pass-vma-instead-of-mm-to-follow_pte.patch
mm-follow_pte-improvements.patch
mm-allow-for-detecting-underflows-with-page_mapcount-again.patch
mm-rmap-always-inline-anon-file-rmap-duplication-of-a-single-pte.patch
mm-rmap-add-fast-path-for-small-folios-when-adding-removing-duplicating.patch
mm-track-mapcount-of-large-folios-in-single-value.patch
mm-improve-folio_likely_mapped_shared-using-the-mapcount-of-large-folios.patch
mm-make-folio_mapcount-return-0-for-small-typed-folios.patch
mm-memory-use-folio_mapcount-in-zap_present_folio_ptes.patch
mm-huge_memory-use-folio_mapcount-in-zap_huge_pmd-sanity-check.patch
mm-memory-failure-use-folio_mapcount-in-hwpoison_user_mappings.patch
mm-page_alloc-use-folio_mapped-in-__alloc_contig_migrate_range.patch
mm-migrate-use-folio_likely_mapped_shared-in-add_page_for_migration.patch
sh-mm-cache-use-folio_mapped-in-copy_from_user_page.patch
mm-filemap-use-folio_mapcount-in-filemap_unaccount_folio.patch
mm-migrate_device-use-folio_mapcount-in-migrate_vma_check_page.patch
trace-events-page_ref-trace-the-raw-page-mapcount-value.patch
xtensa-mm-convert-check_tlb_entry-to-sanity-check-folios.patch
mm-debug-print-only-page-mapcount-excluding-folio-entire-mapcount-in-__dump_folio.patch
documentation-admin-guide-cgroup-v1-memoryrst-dont-reference-page_mapcount.patch
mm-ksm-rename-get_ksm_page_flags-to-ksm_get_folio_flags.patch
mm-ksm-remove-page_mapcount-usage-in-stable_tree_search.patch
loongarch-tlb-fix-error-parameter-ptep-set-but-not-used-due-to-__tlb_remove_tlb_entry.patch
