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From: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Rik van Riel <riel@redhat.com>, Mel Gorman <mgorman@suse.de>,
	Michal Hocko <mhocko@suse.cz>,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	Hugh Dickins <hughd@google.com>,
	Davidlohr Bueso <davidlohr.bueso@hp.com>,
	David Gibson <david@gibson.dropbear.id.au>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Joonsoo Kim <js1304@gmail.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [PATCH 6/9] mm, hugetlb: do not use a page in page cache for cow optimization
Date: Wed, 17 Jul 2013 04:55:09 -0400	[thread overview]
Message-ID: <24020.8320938565$1374051340@news.gmane.org> (raw)
In-Reply-To: <1373881967-16153-7-git-send-email-iamjoonsoo.kim@lge.com>

On Mon, Jul 15, 2013 at 06:52:44PM +0900, Joonsoo Kim wrote:
>Currently, we use a page with mapped count 1 in page cache for cow
>optimization. If we find this condition, we don't allocate a new
>page and copy contents. Instead, we map this page directly.
>This may introduce a problem that writting to private mapping overwrite
>hugetlb file directly. You can find this situation with following code.
>
>        size = 20 * MB;
>        flag = MAP_SHARED;
>        p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, fd, 0);
>        if (p == MAP_FAILED) {
>                fprintf(stderr, "mmap() failed: %s\n", strerror(errno));
>                return -1;
>        }
>        p[0] = 's';
>        fprintf(stdout, "BEFORE STEAL PRIVATE WRITE: %c\n", p[0]);
>        munmap(p, size);
>
>        flag = MAP_PRIVATE;
>        p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, fd, 0);
>        if (p == MAP_FAILED) {
>                fprintf(stderr, "mmap() failed: %s\n", strerror(errno));
>        }
>        p[0] = 'c';
>        munmap(p, size);
>
>        flag = MAP_SHARED;
>        p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, fd, 0);
>        if (p == MAP_FAILED) {
>                fprintf(stderr, "mmap() failed: %s\n", strerror(errno));
>                return -1;
>        }
>        fprintf(stdout, "AFTER STEAL PRIVATE WRITE: %c\n", p[0]);
>        munmap(p, size);
>
>We can see that "AFTER STEAL PRIVATE WRITE: c", not "AFTER STEAL
>PRIVATE WRITE: s". If we turn off this optimization to a page
>in page cache, the problem is disappeared.
>
>Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
>

Good catch!

Reviewed-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>

>diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>index d4a1695..6c1eb9b 100644
>--- a/mm/hugetlb.c
>+++ b/mm/hugetlb.c
>@@ -2512,7 +2512,6 @@ static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
> {
> 	struct hstate *h = hstate_vma(vma);
> 	struct page *old_page, *new_page;
>-	int avoidcopy;
> 	int outside_reserve = 0;
> 	unsigned long mmun_start;	/* For mmu_notifiers */
> 	unsigned long mmun_end;		/* For mmu_notifiers */
>@@ -2522,10 +2521,8 @@ static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
> retry_avoidcopy:
> 	/* If no-one else is actually using this page, avoid the copy
> 	 * and just make the page writable */
>-	avoidcopy = (page_mapcount(old_page) == 1);
>-	if (avoidcopy) {
>-		if (PageAnon(old_page))
>-			page_move_anon_rmap(old_page, vma, address);
>+	if (page_mapcount(old_page) == 1 && PageAnon(old_page)) {
>+		page_move_anon_rmap(old_page, vma, address);
> 		set_huge_ptep_writable(vma, address, ptep);
> 		return 0;
> 	}
>-- 
>1.7.9.5
>
>--
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  parent reply	other threads:[~2013-07-17  8:55 UTC|newest]

Thread overview: 92+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-07-15  9:52 [PATCH 0/9] mm, hugetlb: clean-up and possible bug fix Joonsoo Kim
2013-07-15  9:52 ` Joonsoo Kim
2013-07-15  9:52 ` [PATCH 1/9] mm, hugetlb: move up the code which check availability of free huge page Joonsoo Kim
2013-07-15  9:52   ` Joonsoo Kim
2013-07-15 14:01   ` Aneesh Kumar K.V
2013-07-15 14:01     ` Aneesh Kumar K.V
2013-07-16  1:16     ` Joonsoo Kim
2013-07-16  1:16       ` Joonsoo Kim
2013-07-16  3:36       ` Aneesh Kumar K.V
2013-07-16  3:36         ` Aneesh Kumar K.V
2013-07-16  5:10         ` Joonsoo Kim
2013-07-16  5:10           ` Joonsoo Kim
2013-07-22 14:45   ` Michal Hocko
2013-07-22 14:45     ` Michal Hocko
2013-07-15  9:52 ` [PATCH 2/9] mm, hugetlb: trivial commenting fix Joonsoo Kim
2013-07-15  9:52   ` Joonsoo Kim
2013-07-15 13:12   ` Hillf Danton
2013-07-15 13:12     ` Hillf Danton
2013-07-15 14:02   ` Aneesh Kumar K.V
2013-07-15 14:02     ` Aneesh Kumar K.V
2013-07-22 14:46   ` Michal Hocko
2013-07-22 14:46     ` Michal Hocko
2013-07-15  9:52 ` [PATCH 3/9] mm, hugetlb: clean-up alloc_huge_page() Joonsoo Kim
2013-07-15  9:52   ` Joonsoo Kim
2013-07-22 14:51   ` Michal Hocko
2013-07-22 14:51     ` Michal Hocko
2013-07-23  7:29     ` Joonsoo Kim
2013-07-23  7:29       ` Joonsoo Kim
2013-07-15  9:52 ` [PATCH 4/9] mm, hugetlb: fix and clean-up node iteration code to alloc or free Joonsoo Kim
2013-07-15  9:52   ` Joonsoo Kim
2013-07-15 14:27   ` Aneesh Kumar K.V
2013-07-15 14:27     ` Aneesh Kumar K.V
2013-07-16  1:41     ` Joonsoo Kim
2013-07-16  1:41       ` Joonsoo Kim
2013-07-17  2:00   ` Jianguo Wu
2013-07-17  2:00     ` Jianguo Wu
2013-07-18  6:46     ` Joonsoo Kim
2013-07-18  6:46       ` Joonsoo Kim
2013-07-15  9:52 ` [PATCH 5/9] mm, hugetlb: remove redundant list_empty check in gather_surplus_pages() Joonsoo Kim
2013-07-15  9:52   ` Joonsoo Kim
2013-07-15 14:31   ` Aneesh Kumar K.V
2013-07-15 14:31     ` Aneesh Kumar K.V
2013-07-16  1:42     ` Joonsoo Kim
2013-07-16  1:42       ` Joonsoo Kim
2013-07-22 14:55   ` Michal Hocko
2013-07-22 14:55     ` Michal Hocko
2013-07-15  9:52 ` [PATCH 6/9] mm, hugetlb: do not use a page in page cache for cow optimization Joonsoo Kim
2013-07-15  9:52   ` Joonsoo Kim
2013-07-15 13:55   ` Aneesh Kumar K.V
2013-07-15 13:55     ` Aneesh Kumar K.V
2013-07-16  1:56     ` Joonsoo Kim
2013-07-16  1:56       ` Joonsoo Kim
2013-07-17  8:55   ` Wanpeng Li
2013-07-17  8:55   ` Wanpeng Li [this message]
2013-07-15  9:52 ` [PATCH 7/9] mm, hugetlb: add VM_NORESERVE check in vma_has_reserves() Joonsoo Kim
2013-07-15  9:52   ` Joonsoo Kim
2013-07-15 14:48   ` Aneesh Kumar K.V
2013-07-15 14:48     ` Aneesh Kumar K.V
2013-07-15 15:11   ` Aneesh Kumar K.V
2013-07-15 15:11     ` Aneesh Kumar K.V
2013-07-16  2:12     ` Joonsoo Kim
2013-07-16  2:12       ` Joonsoo Kim
2013-07-16  5:47       ` Aneesh Kumar K.V
2013-07-16  5:47         ` Aneesh Kumar K.V
2013-07-16  7:12         ` Joonsoo Kim
2013-07-16  7:12           ` Joonsoo Kim
2013-07-18  2:03   ` Wanpeng Li
2013-07-18  2:03   ` Wanpeng Li
2013-07-15  9:52 ` [PATCH 8/9] mm, hugetlb: remove decrement_hugepage_resv_vma() Joonsoo Kim
2013-07-15  9:52   ` Joonsoo Kim
2013-07-15 14:50   ` Aneesh Kumar K.V
2013-07-15 14:50     ` Aneesh Kumar K.V
2013-07-17  9:31   ` Wanpeng Li
2013-07-17  9:31   ` Wanpeng Li
2013-07-15  9:52 ` [PATCH 9/9] mm, hugetlb: decrement reserve count if VM_NORESERVE alloc page cache Joonsoo Kim
2013-07-15  9:52   ` Joonsoo Kim
2013-07-15 15:11   ` Aneesh Kumar K.V
2013-07-15 15:11     ` Aneesh Kumar K.V
2013-07-18  2:02   ` Wanpeng Li
2013-07-18  2:02   ` Wanpeng Li
2013-07-15 14:10 ` [PATCH 0/9] mm, hugetlb: clean-up and possible bug fix Aneesh Kumar K.V
2013-07-15 14:10   ` Aneesh Kumar K.V
2013-07-16  1:10   ` Joonsoo Kim
2013-07-16  1:10     ` Joonsoo Kim
2013-07-16  1:27     ` Sam Ben
2013-07-16  1:27       ` Sam Ben
2013-07-16  1:45       ` Joonsoo Kim
2013-07-16  1:45         ` Joonsoo Kim
2013-07-16  1:55         ` Sam Ben
2013-07-16  1:55           ` Sam Ben
2013-07-16  2:14           ` Joonsoo Kim
2013-07-16  2:14             ` Joonsoo Kim

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