Subject: + mm-hugetlb-do-not-use-a-page-in-page-cache-for-cow-optimization.patch added to -mm tree
To: iamjoonsoo.kim@xxxxxxx,aneesh.kumar@xxxxxxxxxxxxxxxxxx,david@xxxxxxxxxxxxxxxxxxxxx,davidlohr.bueso@xxxxxx,dhillf@xxxxxxxxx,hughd@xxxxxxxxxx,kamezawa.hiroyu@xxxxxxxxxxxxxx,liwanp@xxxxxxxxxxxxxxxxxx,mgorman@xxxxxxx,mhocko@xxxxxxx,n-horiguchi@xxxxxxxxxxxxx,riel@xxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Mon, 29 Jul 2013 15:07:53 -0700
The patch titled
Subject: mm, hugetlb: do not use a page in page cache for cow optimization
has been added to the -mm tree. Its filename is
mm-hugetlb-do-not-use-a-page-in-page-cache-for-cow-optimization.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-hugetlb-do-not-use-a-page-in-page-cache-for-cow-optimization.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-hugetlb-do-not-use-a-page-in-page-cache-for-cow-optimization.patch
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From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Subject: mm, hugetlb: do not use a page in page cache for cow optimization
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.
So, I change the trigger condition of optimization. If this page is not
AnonPage, we don't do optimization. This makes this optimization turning
off for a page cache.
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Reviewed-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Acked-by: Hillf Danton <dhillf@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Davidlohr Bueso <davidlohr.bueso@xxxxxx>
Cc: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff -puN mm/hugetlb.c~mm-hugetlb-do-not-use-a-page-in-page-cache-for-cow-optimization mm/hugetlb.c
--- a/mm/hugetlb.c~mm-hugetlb-do-not-use-a-page-in-page-cache-for-cow-optimization
+++ a/mm/hugetlb.c
@@ -2528,7 +2528,6 @@ static int hugetlb_cow(struct mm_struct
{
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 */
@@ -2538,10 +2537,8 @@ static int hugetlb_cow(struct mm_struct
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;
}
_
Patches currently in -mm which might be from iamjoonsoo.kim@xxxxxxx are
mm-hugetlb-move-up-the-code-which-check-availability-of-free-huge-page.patch
mm-hugetlb-trivial-commenting-fix.patch
mm-hugetlb-clean-up-alloc_huge_page.patch
mm-hugetlb-fix-and-clean-up-node-iteration-code-to-alloc-or-free.patch
mm-hugetlb-remove-redundant-list_empty-check-in-gather_surplus_pages.patch
mm-hugetlb-do-not-use-a-page-in-page-cache-for-cow-optimization.patch
mm-hugetlb-add-vm_noreserve-check-in-vma_has_reserves.patch
mm-hugetlb-remove-decrement_hugepage_resv_vma.patch
mm-hugetlb-decrement-reserve-count-if-vm_noreserve-alloc-page-cache.patch
mm-hugetlb-decrement-reserve-count-if-vm_noreserve-alloc-page-cache-fix.patch
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