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mm/migrate: set swap entry values of THP tail pages properly.

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The tail pages in a THP can have swap entry information stored in their
private field. When migrating to a new page, all tail pages of the new
page need to update ->private to avoid future data corruption.

This fix is stable-only, since after commit 07e09c483cbe ("mm/huge_memory:
work on folio->swap instead of page->private when splitting folio"),
subpages of a swapcached THP no longer requires the maintenance.

Adding THPs to the swapcache was introduced in commit
38d8b4e6bd ("mm, THP, swap: delay splitting THP during swap out"),
where each subpage of a THP added to the swapcache had its own swapcache
entry and required the ->private field to point to the correct swapcache
entry. Later, when THP migration functionality was implemented in commit
616b837153 ("mm: thp: enable thp migration in generic path"),
it initially did not handle the subpages of swapcached THPs, failing to
update their ->private fields or replace the subpage pointers in the
swapcache. Subsequently, commit e71769ae52 ("mm: enable thp migration
for shmem thp") addressed the swapcache update aspect. This patch fixes
the update of subpage ->private fields.

Closes: https://lore.kernel.org/linux-mm/1707814102-22682-1-git-send-email-quic_charante@quicinc.com/
Fixes: 616b837153 ("mm: thp: enable thp migration in generic path")
Signed-off-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Zi Yan 2024-03-06 10:51:13 -05:00 • committed by Greg Kroah-Hartman
parent 7f75e937ec
commit 747d4ee747
1 changed files with 5 additions and 1 deletions
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6
mm/migrate.c
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@ -441,8 +441,12 @@ int migrate_page_move_mapping(struct address_space *mapping,
if (PageSwapBacked(page)) {
__SetPageSwapBacked(newpage);
if (PageSwapCache(page)) {
int i;
SetPageSwapCache(newpage);
set_page_private(newpage, page_private(page));
for (i = 0; i < (1 << compound_order(page)); i++)
set_page_private(newpage + i,
page_private(page + i));
}
} else {
VM_BUG_ON_PAGE(PageSwapCache(page), page);