Subject: + mm-hugetlb-add-vm_noreserve-check-in-vma_has_reserves.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 15:07:55 -0700
The patch titled
Subject: mm, hugetlb: add VM_NORESERVE check in vma_has_reserves()
has been added to the -mm tree. Its filename is
mm-hugetlb-add-vm_noreserve-check-in-vma_has_reserves.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-hugetlb-add-vm_noreserve-check-in-vma_has_reserves.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-hugetlb-add-vm_noreserve-check-in-vma_has_reserves.patch
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From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Subject: mm, hugetlb: add VM_NORESERVE check in vma_has_reserves()
If we map the region with MAP_NORESERVE and MAP_SHARED, we can skip to
check reserve counting and eventually we cannot be ensured to allocate a
huge page in fault time. With following example code, you can easily find
this situation.
Assume 2MB, nr_hugepages = 100
fd = hugetlbfs_unlinked_fd();
if (fd < 0)
return 1;
size = 200 * 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;
}
size = 2 * MB;
flag = MAP_ANONYMOUS | MAP_SHARED | MAP_HUGETLB | MAP_NORESERVE;
p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, -1, 0);
if (p == MAP_FAILED) {
fprintf(stderr, "mmap() failed: %s\n", strerror(errno));
}
p[0] = '0';
sleep(10);
During executing sleep(10), run 'cat /proc/meminfo' on another process.
HugePages_Free: 99
HugePages_Rsvd: 100
Number of free should be higher or equal than number of reserve, but this
aren't. This represent that non reserved shared mapping steal a reserved
page. Non reserved shared mapping should not eat into reserve space.
If we consider VM_NORESERVE in vma_has_reserve() and return 0 which mean
that we don't have reserved pages, then we check that we have enough free
pages in dequeue_huge_page_vma(). This prevent to steal a reserved page.
With this change, above test generate a SIGBUG which is correct, because
all free pages are reserved and non reserved shared mapping can't get a
free page.
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Reviewed-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Acked-by: Hillf Danton <dhillf@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
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 | 2 ++
1 file changed, 2 insertions(+)
diff -puN mm/hugetlb.c~mm-hugetlb-add-vm_noreserve-check-in-vma_has_reserves mm/hugetlb.c
--- a/mm/hugetlb.c~mm-hugetlb-add-vm_noreserve-check-in-vma_has_reserves
+++ a/mm/hugetlb.c
@@ -464,6 +464,8 @@ void reset_vma_resv_huge_pages(struct vm
/* Returns true if the VMA has associated reserve pages */
static int vma_has_reserves(struct vm_area_struct *vma)
{
+ if (vma->vm_flags & VM_NORESERVE)
+ return 0;
if (vma->vm_flags & VM_MAYSHARE)
return 1;
if (is_vma_resv_set(vma, HPAGE_RESV_OWNER))
_
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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