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mm: add a signature in struct page

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This is needed by the page_pool to avoid recycling a page not allocated
via page_pool.

The page->signature field is aliased to page->lru.next and
page->compound_head, but it can't be set by mistake because the
signature value is a bad pointer, and can't trigger a false positive
in PageTail() because the last bit is 0.

Co-developed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Matteo Croce <mcroce@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Matteo Croce
2021-06-07 21:02:36 +02:00
committed by David S. Miller
parent 35cba15a50
commit c07aea3ef4
4 changed files with 22 additions and 5 deletions
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11
include/linux/mm.h
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@@ -1668,10 +1668,11 @@ struct address_space *page_mapping(struct page *page);
static inline bool page_is_pfmemalloc(const struct page *page)
{
/*
* Page index cannot be this large so this must be
* a pfmemalloc page.
* lru.next has bit 1 set if the page is allocated from the
* pfmemalloc reserves. Callers may simply overwrite it if
* they do not need to preserve that information.
*/
return page->index == -1UL;
return (uintptr_t)page->lru.next & BIT(1);
}
/*
@@ -1680,12 +1681,12 @@ static inline bool page_is_pfmemalloc(const struct page *page)
*/
static inline void set_page_pfmemalloc(struct page *page)
{
page->index = -1UL;
page->lru.next = (void *)BIT(1);
}
static inline void clear_page_pfmemalloc(struct page *page)
{
page->index = 0;
page->lru.next = NULL;
}
/*