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mm: prep_compound_tail() clear page->private

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Although page allocation always clears page->private in the first page or
head page of an allocation, it has never made a point of clearing
page->private in the tails (though 0 is often what is already there).

But now commit 71e2d666ef ("mm/huge_memory: do not clobber swp_entry_t
during THP split") issues a warning when page_tail->private is found to be
non-0 (unless it's swapcache).

Change that warning to dump page_tail (which also dumps head), instead of
just the head: so far we have seen dead000000000122, dead000000000003,
dead000000000001 or 0000000000000002 in the raw output for tail private.

We could just delete the warning, but today's consensus appears to want
page->private to be 0, unless there's a good reason for it to be set: so
now clear it in prep_compound_tail() (more general than just for THP; but
not for high order allocation, which makes no pass down the tails).

Link: https://lkml.kernel.org/r/1c4233bb-4e4d-5969-fbd4-96604268a285@google.com
Fixes: 71e2d666ef ("mm/huge_memory: do not clobber swp_entry_t during THP split")
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2022-10-22 00:51:06 -07:00 committed by Andrew Morton
parent 8ebe0a5eaa
commit 5aae9265ee
2 changed files with 2 additions and 1 deletions
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2
mm/huge_memory.c
View File

@ -2462,7 +2462,7 @@ static void __split_huge_page_tail(struct page *head, int tail,
* Fix up and warn once if private is unexpectedly set. * Fix up and warn once if private is unexpectedly set.
*/ */
if (!folio_test_swapcache(page_folio(head))) { if (!folio_test_swapcache(page_folio(head))) {
VM_WARN_ON_ONCE_PAGE(page_tail->private != 0, head); VM_WARN_ON_ONCE_PAGE(page_tail->private != 0, page_tail);
page_tail->private = 0; page_tail->private = 0;
} }

1
mm/page_alloc.c
View File

@ -807,6 +807,7 @@ static void prep_compound_tail(struct page *head, int tail_idx)
p->mapping = TAIL_MAPPING; p->mapping = TAIL_MAPPING;
set_compound_head(p, head); set_compound_head(p, head);
set_page_private(p, 0);
} }
void prep_compound_page(struct page *page, unsigned int order) void prep_compound_page(struct page *page, unsigned int order)