> 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>
yes this changelog is much better. Thanks!
Ackedy-by: 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
>
--
Michal Hocko
SUSE Labs
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