From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx112.postini.com [74.125.245.112]) by kanga.kvack.org (Postfix) with SMTP id 7A4D66B0036 for ; Thu, 22 Aug 2013 19:52:47 -0400 (EDT) Received: from /spool/local by e28smtp05.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 23 Aug 2013 05:16:15 +0530 Received: from d28relay02.in.ibm.com (d28relay02.in.ibm.com [9.184.220.59]) by d28dlp03.in.ibm.com (Postfix) with ESMTP id E98881258053 for ; Fri, 23 Aug 2013 05:22:29 +0530 (IST) Received: from d28av01.in.ibm.com (d28av01.in.ibm.com [9.184.220.63]) by d28relay02.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r7MNsH1H40829000 for ; Fri, 23 Aug 2013 05:24:18 +0530 Received: from d28av01.in.ibm.com (localhost [127.0.0.1]) by d28av01.in.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id r7MNqfA9030341 for ; Fri, 23 Aug 2013 05:22:41 +0530 Date: Fri, 23 Aug 2013 07:52:40 +0800 From: Wanpeng Li Subject: Re: [PATCH 3/6] mm/hwpoison: fix num_poisoned_pages error statistics for thp Message-ID: <20130822235239.GA17669@hacker.(null)> Reply-To: Wanpeng Li References: <1377164907-24801-1-git-send-email-liwanp@linux.vnet.ibm.com> <1377164907-24801-3-git-send-email-liwanp@linux.vnet.ibm.com> <1377189788-xv5ewgmb-mutt-n-horiguchi@ah.jp.nec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1377189788-xv5ewgmb-mutt-n-horiguchi@ah.jp.nec.com> Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: Andrew Morton , Andi Kleen , Fengguang Wu , Tony Luck , gong.chen@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Hi Naoya, On Thu, Aug 22, 2013 at 12:43:08PM -0400, Naoya Horiguchi wrote: >On Thu, Aug 22, 2013 at 05:48:24PM +0800, Wanpeng Li wrote: >> There is a race between hwpoison page and unpoison page, memory_failure >> set the page hwpoison and increase num_poisoned_pages without hold page >> lock, and one page count will be accounted against thp for num_poisoned_pages. >> However, unpoison can occur before memory_failure hold page lock and >> split transparent hugepage, unpoison will decrease num_poisoned_pages >> by 1 << compound_order since memory_failure has not yet split transparent >> hugepage with page lock held. That means we account one page for hwpoison >> and 1 << compound_order for unpoison. This patch fix it by decrease one >> account for num_poisoned_pages against no hugetlbfs pages case. >> >> Signed-off-by: Wanpeng Li > >I think that a thp never becomes hwpoisoned without splitting, so "trying >to unpoison thp" never happens (I think that this implicit fact should be There is a race window here for hwpoison thp: A B memory_failue TestSetPageHWPoison(p); if (PageHuge(p)) nr_pages = 1 << compound_order(hpage); else nr_pages = 1; atomic_long_add(nr_pages, &num_poisoned_pages); unpoison_memory nr_pages = 1<< compound_trans_order(page;) if(TestClearPageHWPoison(p)) atomic_long_sub(nr_pages, &num_poisoned_pages); lock page if (!PageHWPoison(p)) unlock page and return hwpoison_user_mappings if (PageTransHuge(hpage)) split_huge_page(hpage); We increase one page count, however, decrease 1 << compound_trans_order. The compound_trans_order you mentioned is used here for thp, that's why I don't drop it in patch 2/6. >commented somewhere or asserted with VM_BUG_ON().) I will add the VM_BUG_ON() in unpoison_memory after lock page in next version. >And nr_pages in unpoison_memory() can be greater than 1 for hugetlbfs page. >So does this patch break counting when unpoisoning free hugetlbfs pages? > >Thanks, >Naoya Horiguchi > >> --- >> mm/memory-failure.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >> index 5092e06..6bfd51e 100644 >> --- a/mm/memory-failure.c >> +++ b/mm/memory-failure.c >> @@ -1350,7 +1350,7 @@ int unpoison_memory(unsigned long pfn) >> return 0; >> } >> if (TestClearPageHWPoison(p)) >> - atomic_long_sub(nr_pages, &num_poisoned_pages); >> + atomic_long_dec(&num_poisoned_pages); >> pr_info("MCE: Software-unpoisoned free page %#lx\n", pfn); >> return 0; >> } >> -- >> 1.8.1.2 >> -- 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