From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1162515Ab3DES7r (ORCPT ); Fri, 5 Apr 2013 14:59:47 -0400 Received: from mail-ye0-f177.google.com ([209.85.213.177]:50434 "EHLO mail-ye0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1162497Ab3DES7p (ORCPT ); Fri, 5 Apr 2013 14:59:45 -0400 X-Greylist: delayed 1240 seconds by postgrey-1.27 at vger.kernel.org; Fri, 05 Apr 2013 14:59:45 EDT Message-ID: <515F1F1F.6060900@gmail.com> Date: Fri, 05 Apr 2013 14:59:43 -0400 From: KOSAKI Motohiro User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:17.0) Gecko/20130307 Thunderbird/17.0.4 MIME-Version: 1.0 To: Naoya Horiguchi CC: Andrew Morton , Mel Gorman , Hugh Dickins , Rik van Riel , KOSAKI Motohiro , Konstantin Khlebnikov , Michal Hocko , HATAYAMA Daisuke , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kosaki.motohiro@gmail.com Subject: Re: [PATCH v3 3/3] hugetlbfs: add swap entry check in follow_hugetlb_page() References: <1365014138-19589-1-git-send-email-n-horiguchi@ah.jp.nec.com> <1365014138-19589-4-git-send-email-n-horiguchi@ah.jp.nec.com> In-Reply-To: <1365014138-19589-4-git-send-email-n-horiguchi@ah.jp.nec.com> Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (4/3/13 2:35 PM), Naoya Horiguchi wrote: > With applying the previous patch "hugetlbfs: stop setting VM_DONTDUMP in > initializing vma(VM_HUGETLB)" to reenable hugepage coredump, if a memory > error happens on a hugepage and the affected processes try to access > the error hugepage, we hit VM_BUG_ON(atomic_read(&page->_count) <= 0) > in get_page(). > > The reason for this bug is that coredump-related code doesn't recognise > "hugepage hwpoison entry" with which a pmd entry is replaced when a memory > error occurs on a hugepage. > In other words, physical address information is stored in different bit layout > between hugepage hwpoison entry and pmd entry, so follow_hugetlb_page() > which is called in get_dump_page() returns a wrong page from a given address. > > We need to filter out only hwpoison hugepages to have data on healthy > hugepages in coredump. So this patch makes follow_hugetlb_page() avoid > trying to get page when a pmd is in swap entry like format. > > ChangeLog v3: > - add comment about using is_swap_pte() > > Signed-off-by: Naoya Horiguchi > Reviewed-by: Michal Hocko > Acked-by: Konstantin Khlebnikov > Cc: stable@vger.kernel.org > --- > mm/hugetlb.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git v3.9-rc3.orig/mm/hugetlb.c v3.9-rc3/mm/hugetlb.c > index 0d1705b..3bc20bd 100644 > --- v3.9-rc3.orig/mm/hugetlb.c > +++ v3.9-rc3/mm/hugetlb.c > @@ -2966,9 +2966,15 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, > * Some archs (sparc64, sh*) have multiple pte_ts to > * each hugepage. We have to make sure we get the > * first, for the page indexing below to work. > + * > + * is_swap_pte test covers both is_hugetlb_entry_hwpoisoned > + * and hugepages under migration in which case > + * hugetlb_fault waits for the migration and bails out > + * properly for HWPosined pages. > */ > pte = huge_pte_offset(mm, vaddr & huge_page_mask(h)); > - absent = !pte || huge_pte_none(huge_ptep_get(pte)); > + absent = !pte || huge_pte_none(huge_ptep_get(pte)) || > + is_swap_pte(huge_ptep_get(pte)); Hmmm... Now absent has two meanings. 1) skip hugetlb_fault() and return immediately if FOLL_DUMP is used. 2) call hugetlb_fault() if to be need page population or cow. The description of this patch only explain about (2). and I'm not convinced why we don't need to dump pages under migraion.