From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx105.postini.com [74.125.245.105]) by kanga.kvack.org (Postfix) with SMTP id BAB016B0036 for ; Wed, 17 Jul 2013 22:04:07 -0400 (EDT) Received: from /spool/local by e23smtp03.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 18 Jul 2013 11:54:00 +1000 Received: from d23relay05.au.ibm.com (d23relay05.au.ibm.com [9.190.235.152]) by d23dlp01.au.ibm.com (Postfix) with ESMTP id 51BAD2CE802D for ; Thu, 18 Jul 2013 12:04:01 +1000 (EST) Received: from d23av01.au.ibm.com (d23av01.au.ibm.com [9.190.234.96]) by d23relay05.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r6I1mZOg852472 for ; Thu, 18 Jul 2013 11:48:35 +1000 Received: from d23av01.au.ibm.com (loopback [127.0.0.1]) by d23av01.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r6I23xL0026920 for ; Thu, 18 Jul 2013 12:04:00 +1000 Date: Wed, 17 Jul 2013 22:03:58 -0400 From: Wanpeng Li Subject: Re: [PATCH 7/9] mm, hugetlb: add VM_NORESERVE check in vma_has_reserves() Message-ID: <20130718020358.GB10133@hacker.(null)> Reply-To: Wanpeng Li References: <1373881967-16153-1-git-send-email-iamjoonsoo.kim@lge.com> <1373881967-16153-8-git-send-email-iamjoonsoo.kim@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1373881967-16153-8-git-send-email-iamjoonsoo.kim@lge.com> 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 On Mon, Jul 15, 2013 at 06:52:45PM +0900, 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. >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. > Reviewed-by: Wanpeng Li >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, 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 -- 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