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thp: keep huge zero page pinned until tlb flush

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Andrea has found[1] a race condition on MMU-gather based TLB flush vs
split_huge_page() or shrinker which frees huge zero under us (patch 1/2
and 2/2 respectively).

With new THP refcounting, we don't need patch 1/2: mmu_gather keeps the
page pinned until flush is complete and the pin prevents the page from
being split under us.

We still need patch 2/2.  This is simplified version of Andrea's patch.
We don't need fancy encoding.

[1] http://lkml.kernel.org/r/1447938052-22165-1-git-send-email-aarcange@redhat.com

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
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 2016-04-28 16:18:27 -07:00 committed by Linus Torvalds
parent 66ee95d16a
commit aa88b68c3b
3 changed files with 13 additions and 3 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

5
include/linux/huge_mm.h
View file

@ -152,6 +152,7 @@ static inline bool is_huge_zero_pmd(pmd_t pmd)
}
struct page *get_huge_zero_page(void);
void put_huge_zero_page(void);
#else /* CONFIG_TRANSPARENT_HUGEPAGE */
#define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
@ -208,6 +209,10 @@ static inline bool is_huge_zero_page(struct page *page)
return false;
}
static inline void put_huge_zero_page(void)
{
BUILD_BUG();
}
static inline struct page *follow_devmap_pmd(struct vm_area_struct *vma,
unsigned long addr, pmd_t *pmd, int flags)

6
mm/huge_memory.c
View file

@ -232,7 +232,7 @@ struct page *get_huge_zero_page(void)
return READ_ONCE(huge_zero_page);
}
static void put_huge_zero_page(void)
void put_huge_zero_page(void)
{
/*
* Counter should never go to zero here. Only shrinker can put
@ -1684,12 +1684,12 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
if (vma_is_dax(vma)) {
spin_unlock(ptl);
if (is_huge_zero_pmd(orig_pmd))
put_huge_zero_page();
tlb_remove_page(tlb, pmd_page(orig_pmd));
} else if (is_huge_zero_pmd(orig_pmd)) {
pte_free(tlb->mm, pgtable_trans_huge_withdraw(tlb->mm, pmd));
atomic_long_dec(&tlb->mm->nr_ptes);
spin_unlock(ptl);
put_huge_zero_page();
tlb_remove_page(tlb, pmd_page(orig_pmd));
} else {
struct page *page = pmd_page(orig_pmd);
page_remove_rmap(page, true);

5
mm/swap.c
View file

@ -728,6 +728,11 @@ void release_pages(struct page **pages, int nr, bool cold)
zone = NULL;
}
if (is_huge_zero_page(page)) {
put_huge_zero_page();
continue;
}
page = compound_head(page);
if (!put_page_testzero(page))
continue;