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authorDavid Hildenbrand <david@redhat.com>2022-03-24 18:13:37 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2022-03-24 19:06:50 -0700
commit84d60fdd3733fb86c126f2adfd0361fdc44087c3 (patch)
tree15e2099fb11e5f144c1cb51ac00994b4c234a352 /mm
parentd4c470970d45c863fafc757521a82be2f80b1232 (diff)
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. [akpm@linux-foundation.org: fix comment, per David] Link: https://lkml.kernel.org/r/20220131162940.210846-4-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: David Rientjes <rientjes@google.com> Cc: Don Dutile <ddutile@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Liang Zhang <zhangliang5@huawei.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Peter Xu <peterx@redhat.com> Cc: Rik van Riel <riel@surriel.com> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Shakeel Butt <shakeelb@google.com> Cc: Yang Shi <shy828301@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/memory.c38
1 files changed, 23 insertions, 15 deletions
diff --git a/mm/memory.c b/mm/memory.c
index c7723bdaf0c3..8e30675dc077 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3607,21 +3607,29 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
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;
-
- page = ksm_might_need_to_copy(page, vma, vmf->address);
- if (unlikely(!page)) {
- ret = VM_FAULT_OOM;
- page = swapcache;
- goto out_page;
+ if (swapcache) {
+ /*
+ * Make sure try_to_free_swap 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;
+
+ /*
+ * 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);