From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx127.postini.com [74.125.245.127]) by kanga.kvack.org (Postfix) with SMTP id 40E4A6B0031 for ; Mon, 29 Jul 2013 05:34:54 -0400 (EDT) Received: by mail-ob0-f171.google.com with SMTP id tb18so8882504obb.16 for ; Mon, 29 Jul 2013 02:34:53 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1375075701-5998-8-git-send-email-iamjoonsoo.kim@lge.com> References: <1375075701-5998-1-git-send-email-iamjoonsoo.kim@lge.com> <1375075701-5998-8-git-send-email-iamjoonsoo.kim@lge.com> Date: Mon, 29 Jul 2013 17:34:53 +0800 Message-ID: Subject: Re: [PATCH v3 7/9] mm, hugetlb: add VM_NORESERVE check in vma_has_reserves() From: Hillf Danton Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Joonsoo Kim Cc: Andrew Morton , Rik van Riel , Mel Gorman , Michal Hocko , "Aneesh Kumar K.V" , KAMEZAWA Hiroyuki , Hugh Dickins , Davidlohr Bueso , David Gibson , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim , Wanpeng Li , Naoya Horiguchi On Mon, Jul 29, 2013 at 1:28 PM, Joonsoo Kim wrote: > 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. > > Reviewed-by: Wanpeng Li > Reviewed-by: Aneesh Kumar K.V > Signed-off-by: Joonsoo Kim > Acked-by: Hillf Danton > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 1f6b3a6..ca15854 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 > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org