Messages in this thread Patch in this message | | | From | Joonsoo Kim <> | Subject | [PATCH 7/9] mm, hugetlb: add VM_NORESERVE check in vma_has_reserves() | Date | Mon, 15 Jul 2013 18:52:45 +0900 |
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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. You'll find a mentioned problem.
Solution is simple. We should check VM_NORESERVE in vma_has_reserves(). This prevent to use a pre-allocated huge page if free count is under the reserve count.
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 6c1eb9b..f6a7a4e 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -464,6 +464,8 @@ void reset_vma_resv_huge_pages(struct vm_area_struct *vma) /* 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)) -- 1.7.9.5
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