From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx197.postini.com [74.125.245.197]) by kanga.kvack.org (Postfix) with SMTP id CEE836B0032 for ; Tue, 23 Jul 2013 00:26:29 -0400 (EDT) Date: Tue, 23 Jul 2013 00:26:07 -0400 From: Naoya Horiguchi Message-ID: <1374553567-p2x98j9o-mutt-n-horiguchi@ah.jp.nec.com> In-Reply-To: <1374482191-3500-8-git-send-email-iamjoonsoo.kim@lge.com> References: <1374482191-3500-1-git-send-email-iamjoonsoo.kim@lge.com> <1374482191-3500-8-git-send-email-iamjoonsoo.kim@lge.com> Subject: Re: [PATCH v2 07/10] mm, hugetlb: do not use a page in page cache for cow optimization Mime-Version: 1.0 Content-Type: text/plain; charset=iso-2022-jp Content-Transfer-Encoding: 7bit Content-Disposition: inline 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 22, 2013 at 05:36:28PM +0900, Joonsoo Kim wrote: > Currently, we use a page with mapped count 1 in page cache for cow > optimization. If we find this condition, we don't allocate a new > page and copy contents. Instead, we map this page directly. > This may introduce a problem that writting to private mapping overwrite > hugetlb file directly. You can find this situation with following code. > > size = 20 * 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; > } > p[0] = 's'; > fprintf(stdout, "BEFORE STEAL PRIVATE WRITE: %c\n", p[0]); > munmap(p, size); > > flag = MAP_PRIVATE; > p = mmap(NULL, size, PROT_READ|PROT_WRITE, flag, fd, 0); > if (p == MAP_FAILED) { > fprintf(stderr, "mmap() failed: %s\n", strerror(errno)); > } > p[0] = 'c'; > munmap(p, size); > > 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; > } > fprintf(stdout, "AFTER STEAL PRIVATE WRITE: %c\n", p[0]); > munmap(p, size); > > We can see that "AFTER STEAL PRIVATE WRITE: c", not "AFTER STEAL > PRIVATE WRITE: s". If we turn off this optimization to a page > in page cache, the problem is disappeared. Looks good to me. Thanks for the fix. Reviewed-by: Naoya Horiguchi > Reviewed-by: Wanpeng Li > Signed-off-by: Joonsoo Kim > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 7ca8733..8a61638 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -2508,7 +2508,6 @@ static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma, > { > struct hstate *h = hstate_vma(vma); > struct page *old_page, *new_page; > - int avoidcopy; > int outside_reserve = 0; > unsigned long mmun_start; /* For mmu_notifiers */ > unsigned long mmun_end; /* For mmu_notifiers */ > @@ -2518,10 +2517,8 @@ static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma, > retry_avoidcopy: > /* If no-one else is actually using this page, avoid the copy > * and just make the page writable */ > - avoidcopy = (page_mapcount(old_page) == 1); > - if (avoidcopy) { > - if (PageAnon(old_page)) > - page_move_anon_rmap(old_page, vma, address); > + if (page_mapcount(old_page) == 1 && PageAnon(old_page)) { > + page_move_anon_rmap(old_page, vma, address); > set_huge_ptep_writable(vma, address, ptep); > return 0; > } > -- > 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