The patch titled Subject: mm: prep_compound_tail() clear page->private has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-prep_compound_tail-clear-page-private.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------ From: Hugh Dickins hughd@google.com Subject: mm: prep_compound_tail() clear page->private Date: Sat, 22 Oct 2022 00:51:06 -0700 (PDT)
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 71e2d666ef85 ("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: 71e2d666ef85 ("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 ---
mm/huge_memory.c | 2 +- mm/page_alloc.c | 1 + 2 files changed, 2 insertions(+), 1 deletion(-)
--- a/mm/huge_memory.c~mm-prep_compound_tail-clear-page-private +++ a/mm/huge_memory.c @@ -2462,7 +2462,7 @@ static void __split_huge_page_tail(struc * Fix up and warn once if private is unexpectedly set. */ 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; }
--- a/mm/page_alloc.c~mm-prep_compound_tail-clear-page-private +++ a/mm/page_alloc.c @@ -807,6 +807,7 @@ static void prep_compound_tail(struct pa
p->mapping = TAIL_MAPPING; set_compound_head(p, head); + set_page_private(p, 0); }
void prep_compound_page(struct page *page, unsigned int order) _
Patches currently in -mm which might be from hughd@google.com are
mm-prep_compound_tail-clear-page-private.patch