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thp: alter compound get_page/put_page

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Alter compound get_page/put_page to keep references on subpages too, in
order to allow __split_huge_page_refcount to split an hugepage even while
subpages have been pinned by one of the get_user_pages() variants.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrea Arcangeli 2011-01-13 15:46:32 -08:00 • committed by Linus Torvalds
parent e9da73d677
commit 9180706344
4 changed files with 129 additions and 9 deletions
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24
include/linux/mm.h
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@ -353,9 +353,29 @@ static inline int page_count(struct page *page)
static inline void get_page(struct page *page)
{
page = compound_head(page);
VM_BUG_ON(atomic_read(&page->_count) == 0);
/*
* Getting a normal page or the head of a compound page
* requires to already have an elevated page->_count. Only if
* we're getting a tail page, the elevated page->_count is
* required only in the head page, so for tail pages the
* bugcheck only verifies that the page->_count isn't
* negative.
*/
VM_BUG_ON(atomic_read(&page->_count) < !PageTail(page));
atomic_inc(&page->_count);
/*
* Getting a tail page will elevate both the head and tail
* page->_count(s).
*/
if (unlikely(PageTail(page))) {
/*
* This is safe only because
* __split_huge_page_refcount can't run under
* get_page().
*/
VM_BUG_ON(atomic_read(&page->first_page->_count) <= 0);
atomic_inc(&page->first_page->_count);
}
}
static inline struct page *virt_to_head_page(const void *x)