From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932485Ab3GWNXJ (ORCPT ); Tue, 23 Jul 2013 09:23:09 -0400 Received: from cantor2.suse.de ([195.135.220.15]:40011 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756432Ab3GWNXH (ORCPT ); Tue, 23 Jul 2013 09:23:07 -0400 Date: Tue, 23 Jul 2013 15:23:02 +0200 From: Michal Hocko To: Joonsoo Kim Cc: Andrew Morton , Rik van Riel , Mel Gorman , "Aneesh Kumar K.V" , KAMEZAWA Hiroyuki , Hugh Dickins , Davidlohr Bueso , David Gibson , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim Subject: Re: [PATCH v2 08/10] mm, hugetlb: add VM_NORESERVE check in vma_has_reserves() Message-ID: <20130723132302.GC8677@dhcp22.suse.cz> References: <1374482191-3500-1-git-send-email-iamjoonsoo.kim@lge.com> <1374482191-3500-9-git-send-email-iamjoonsoo.kim@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1374482191-3500-9-git-send-email-iamjoonsoo.kim@lge.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 22-07-13 17:36:29, 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. > > non reserved shared mapping should not eat into reserve space. So > return error when we don't find enough free space. I guess I undestand what you are trying to tell but the changelog is really hard to read. Please be explicit about what is the expected result of the test and what is the fix doing. The reservation code is quite complex already. > Reviewed-by: Wanpeng Li > Reviewed-by: Aneesh Kumar K.V > Signed-off-by: Joonsoo Kim > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 8a61638..87e73bd 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 > -- Michal Hocko SUSE Labs