Commit aa88b68c authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds
Browse files

thp: keep huge zero page pinned until tlb flush 

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: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
Reviewed-by: default avatarAndrea 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 66ee95d1

include/linux/huge_mm.h

+5 −0
Original line number Original line Diff line number Diff line
@@ -152,6 +152,7 @@ static inline bool is_huge_zero_pmd(pmd_t pmd) 
}

}





struct page *get_huge_zero_page(void);

struct page *get_huge_zero_page(void);

void put_huge_zero_page(void);





#else /* CONFIG_TRANSPARENT_HUGEPAGE */

#else /* CONFIG_TRANSPARENT_HUGEPAGE */

#define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })

#define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
@@ -208,6 +209,10 @@ static inline bool is_huge_zero_page(struct page *page) 
	return false;

	return false;

}

}





static inline void put_huge_zero_page(void)

{

	BUILD_BUG();

}





static inline struct page *follow_devmap_pmd(struct vm_area_struct *vma,

static inline struct page *follow_devmap_pmd(struct vm_area_struct *vma,

		unsigned long addr, pmd_t *pmd, int flags)

		unsigned long addr, pmd_t *pmd, int flags)

mm/huge_memory.c

+3 −3
Original line number Original line Diff line number Diff line
@@ -232,7 +232,7 @@ retry: 
	return READ_ONCE(huge_zero_page);

	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

	 * 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)) {

	if (vma_is_dax(vma)) {

		spin_unlock(ptl);

		spin_unlock(ptl);

		if (is_huge_zero_pmd(orig_pmd))

		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)) {

	} else if (is_huge_zero_pmd(orig_pmd)) {

		pte_free(tlb->mm, pgtable_trans_huge_withdraw(tlb->mm, pmd));

		pte_free(tlb->mm, pgtable_trans_huge_withdraw(tlb->mm, pmd));

		atomic_long_dec(&tlb->mm->nr_ptes);

		atomic_long_dec(&tlb->mm->nr_ptes);

		spin_unlock(ptl);

		spin_unlock(ptl);

		put_huge_zero_page();

		tlb_remove_page(tlb, pmd_page(orig_pmd));

	} else {

	} else {

		struct page *page = pmd_page(orig_pmd);

		struct page *page = pmd_page(orig_pmd);

		page_remove_rmap(page, true);

		page_remove_rmap(page, true);

mm/swap.c

+5 −0
Original line number Original line Diff line number Diff line
@@ -728,6 +728,11 @@ void release_pages(struct page **pages, int nr, bool cold) 
			zone = NULL;

			zone = NULL;

		}

		}





		if (is_huge_zero_page(page)) {

			put_huge_zero_page();

			continue;

		}



		page = compound_head(page);

		page = compound_head(page);

		if (!put_page_testzero(page))

		if (!put_page_testzero(page))

			continue;

			continue;

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