Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932557Ab3GOPL2 (ORCPT ); Mon, 15 Jul 2013 11:11:28 -0400 Received: from e23smtp09.au.ibm.com ([202.81.31.142]:38503 "EHLO e23smtp09.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932531Ab3GOPLZ (ORCPT ); Mon, 15 Jul 2013 11:11:25 -0400 From: "Aneesh Kumar K.V" To: Joonsoo Kim , Andrew Morton Cc: Rik van Riel , Mel Gorman , Michal Hocko , KAMEZAWA Hiroyuki , Hugh Dickins , Davidlohr Bueso , David Gibson , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim , Joonsoo Kim Subject: Re: [PATCH 7/9] mm, hugetlb: add VM_NORESERVE check in vma_has_reserves() In-Reply-To: <1373881967-16153-8-git-send-email-iamjoonsoo.kim@lge.com> References: <1373881967-16153-1-git-send-email-iamjoonsoo.kim@lge.com> <1373881967-16153-8-git-send-email-iamjoonsoo.kim@lge.com> User-Agent: Notmuch/0.15.2+167~g5306b2b (http://notmuchmail.org) Emacs/24.3.50.1 (x86_64-unknown-linux-gnu) Date: Mon, 15 Jul 2013 20:41:12 +0530 Message-ID: <87li57j1tb.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13071602-3568-0000-0000-000003ED97AB Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2405 Lines: 72 Joonsoo Kim writes: > 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. You have a problem with this patch, which i guess you are fixing in patch 9. Consider two process a) MAP_SHARED on fd b) MAP_SHARED | MAP_NORESERVE on fd We should allow the (b) to access the page even if VM_NORESERVE is set and we are out of reserve space . so may be you should rearrange the patch ? > > Signed-off-by: Joonsoo Kim > > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/