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mm-slightly-clarify-ksm-logic-in-do_swap_page.patch removed from -mm tree

merged Andrew Morton 1 participant 1 message Mar 25, 2022

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The patch titled
Subject: mm: slightly clarify KSM logic in do_swap_page()
has been removed from the -mm tree. Its filename was
mm-slightly-clarify-ksm-logic-in-do_swap_page.patch

This patch was dropped because it was merged into mainline or a subsystem tree

------------------------------------------------------
From: David Hildenbrand <[email protected]>
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.

[[email protected]: fix comment, per David]
Link https://lkml.kernel.org/r/[email protected] open here
Signed-off-by David Hildenbrand <[email protected]>
Acked-by Vlastimil Babka <[email protected]>
Cc Andrea Arcangeli <[email protected]>
Cc Christoph Hellwig <[email protected]>
Cc David Rientjes <[email protected]>
Cc Don Dutile <[email protected]>
Cc Hugh Dickins <[email protected]>
Cc Jan Kara <[email protected]>
Cc Jann Horn <[email protected]>
Cc Jason Gunthorpe <[email protected]>
Cc John Hubbard <[email protected]>
Cc Kirill A. Shutemov <[email protected]>
Cc Liang Zhang <[email protected]>
Cc Matthew Wilcox (Oracle) <[email protected]>
Cc Michal Hocko <[email protected]>
Cc Mike Kravetz <[email protected]>
Cc Mike Rapoport <[email protected]>
Cc Nadav Amit <[email protected]>
Cc Oleg Nesterov <[email protected]>
Cc Peter Xu <[email protected]>
Cc Rik van Riel <[email protected]>
Cc Roman Gushchin <[email protected]>
Cc Shakeel Butt <[email protected]>
Cc Yang Shi <[email protected]>
Signed-off-by Andrew Morton <[email protected]>

---

 mm/memory.c |   36 ++++++++++++++++++++++--------------
 1 file changed, 22 insertions(+), 14 deletions(-)
mm/memory.c renamed from mm/memory.c~mm-slightly-clarify-ksm-logic-in-do_swap_page +22 -14
@@ -3607,21 +3607,29 @@ 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 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 [email protected] are