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mm: handle PTE-mapped tail pages in gerneric fast gup implementaiton 

With new refcounting we are going to see THP tail pages mapped with PTE.
Generic fast GUP rely on page_cache_get_speculative() to obtain
reference on page.  page_cache_get_speculative() always fails on tail
pages, because ->_count on tail pages is always zero.

Let's handle tail pages in gup_pte_range().

New split_huge_page() will rely on migration entries to freeze page's
counts.  Recheck PTE value after page_cache_get_speculative() on head
page should be enough to serialize against split.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Steve Capper <steve.capper@linaro.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kirill A. Shutemov 2016-01-15 16:52:32 -08:00 committed by Linus Torvalds
parent 6742d293cb
commit 7aef4172c7
1 changed files with 5 additions and 3 deletions
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8
mm/gup.c
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@ -1097,7 +1097,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
* for an example see gup_get_pte in arch/x86/mm/gup.c
*/
pte_t pte = READ_ONCE(*ptep);
struct page *page;
struct page *head, *page;
/*
* Similar to the PMD case below, NUMA hinting must take slow
@ -1109,15 +1109,17 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
page = pte_page(pte);
head = compound_head(page);
if (!page_cache_get_speculative(page))
if (!page_cache_get_speculative(head))
goto pte_unmap;
if (unlikely(pte_val(pte) != pte_val(*ptep))) {
put_page(page);
put_page(head);
goto pte_unmap;
}
VM_BUG_ON_PAGE(compound_head(page) != head, page);
pages[*nr] = page;
(*nr)++;