The patch titled
Subject: mm: slightly clarify KSM logic in do_swap_page()
has been added to the -mm tree. Its filename is
mm-slightly-clarify-ksm-logic-in-do_swap_page.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-slightly-clarify-ksm-logic-in-do_swap_page.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-slightly-clarify-ksm-logic-in-do_swap_page.patch
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm: slightly clarify KSM logic in do_swap_page()
Let's make it clearer that KSM might only have to copy a page in case we
have a page in the swapcache, not if we allocated a fresh page and
bypassed the swapcache. While at it, add a comment why this is usually
necessary and merge the two swapcache conditions.
Link: https://lkml.kernel.org/r/20220131162940.210846-4-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Don Dutile <ddutile@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Liang Zhang <zhangliang5@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Cc: Nadav Amit <nadav.amit@xxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 36 ++++++++++++++++++++++--------------
1 file changed, 22 insertions(+), 14 deletions(-)
--- a/mm/memory.c~mm-slightly-clarify-ksm-logic-in-do_swap_page
+++ a/mm/memory.c
@@ -3615,21 +3615,29 @@ vm_fault_t do_swap_page(struct vm_fault
goto out_release;
}
- /*
- * Make sure try_to_free_swap or reuse_swap_page or swapoff did not
- * release the swapcache from under us. The page pin, and pte_same
- * test below, are not enough to exclude that. Even if it is still
- * swapcache, we need to check that the page's swap has not changed.
- */
- if (unlikely((!PageSwapCache(page) ||
- page_private(page) != entry.val)) && swapcache)
- goto out_page;
+ if (swapcache) {
+ /*
+ * Make sure try_to_free_swap or reuse_swap_page or swapoff did
+ * not release the swapcache from under us. The page pin, and
+ * pte_same test below, are not enough to exclude that. Even if
+ * it is still swapcache, we need to check that the page's swap
+ * has not changed.
+ */
+ if (unlikely(!PageSwapCache(page) ||
+ page_private(page) != entry.val))
+ goto out_page;
- page = ksm_might_need_to_copy(page, vma, vmf->address);
- if (unlikely(!page)) {
- ret = VM_FAULT_OOM;
- page = swapcache;
- goto out_page;
+ /*
+ * KSM sometimes has to copy on read faults, for example, if
+ * page->index of !PageKSM() pages would be nonlinear inside the
+ * anon VMA -- PageKSM() is lost on actual swapout.
+ */
+ page = ksm_might_need_to_copy(page, vma, vmf->address);
+ if (unlikely(!page)) {
+ ret = VM_FAULT_OOM;
+ page = swapcache;
+ goto out_page;
+ }
}
cgroup_throttle_swaprate(page, GFP_KERNEL);
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-optimize-do_wp_page-for-exclusive-pages-in-the-swapcache.patch
mm-optimize-do_wp_page-for-fresh-pages-in-local-lru-pagevecs.patch
mm-slightly-clarify-ksm-logic-in-do_swap_page.patch
mm-streamline-cow-logic-in-do_swap_page.patch
mm-huge_memory-streamline-cow-logic-in-do_huge_pmd_wp_page.patch
mm-khugepaged-remove-reuse_swap_page-usage.patch
mm-swapfile-remove-stale-reuse_swap_page.patch
mm-huge_memory-remove-stale-page_trans_huge_mapcount.patch
mm-huge_memory-remove-stale-locking-logic-from-__split_huge_pmd.patch
proc-vmcore-fix-possible-deadlock-on-concurrent-mmap-and-read.patch
