From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752506AbeBIEry (ORCPT ); Thu, 8 Feb 2018 23:47:54 -0500 Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:50875 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752154AbeBIErw (ORCPT ); Thu, 8 Feb 2018 23:47:52 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R421e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04421;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0SxvBcog_1518151655; Subject: Re: [PATCH] mm: thp: fix potential clearing to referenced flag in page_idle_clear_pte_refs_one() To: "Kirill A. Shutemov" , Andrew Morton Cc: kirill.shutemov@linux.intel.com, gavin.dg@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1517875596-76350-1-git-send-email-yang.shi@linux.alibaba.com> <20180208143926.5484e8fd75a56ff35b778bcc@linux-foundation.org> <20180209043325.l6b6hwgeomqldeb6@node.shutemov.name> From: Yang Shi Message-ID: Date: Thu, 8 Feb 2018 20:47:35 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20180209043325.l6b6hwgeomqldeb6@node.shutemov.name> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/8/18 8:33 PM, Kirill A. Shutemov wrote: > On Thu, Feb 08, 2018 at 02:39:26PM -0800, Andrew Morton wrote: >> On Tue, 6 Feb 2018 08:06:36 +0800 Yang Shi wrote: >> >>> For PTE-mapped THP, the compound THP has not been split to normal 4K >>> pages yet, the whole THP is considered referenced if any one of sub >>> page is referenced. >>> >>> When walking PTE-mapped THP by pvmw, all relevant PTEs will be checked >>> to retrieve referenced bit. But, the current code just returns the >>> result of the last PTE. If the last PTE has not referenced, the >>> referenced flag will be cleared. >>> >>> So, here just break pvmw walk once referenced PTE is found if the page >>> is a part of THP. >>> >>> ... >>> >>> --- a/mm/page_idle.c >>> +++ b/mm/page_idle.c >>> @@ -67,6 +67,14 @@ static bool page_idle_clear_pte_refs_one(struct page *page, >>> if (pvmw.pte) { >>> referenced = ptep_clear_young_notify(vma, addr, >>> pvmw.pte); >>> + /* >>> + * For PTE-mapped THP, one sub page is referenced, >>> + * the whole THP is referenced. >>> + */ >>> + if (referenced && PageTransCompound(pvmw.page)) { >>> + page_vma_mapped_walk_done(&pvmw); >>> + break; >>> + } >> This means that the function will no longer clear the referenced bits >> in all the ptes. What effect does this have and should we document >> this in some fashion? > Yeah, the patch is wrong. We need to get all ptes for THP cleared. > > What about something like this instead (untested): Thanks, Kirill. It looks correct. All ptes should be cleared. I'm going to prepare v2 patch. Regards, Yang > > diff --git a/mm/page_idle.c b/mm/page_idle.c > index 0a49374e6931..6876522c9dce 100644 > --- a/mm/page_idle.c > +++ b/mm/page_idle.c > @@ -65,10 +65,10 @@ static bool page_idle_clear_pte_refs_one(struct page *page, > while (page_vma_mapped_walk(&pvmw)) { > addr = pvmw.address; > if (pvmw.pte) { > - referenced = ptep_clear_young_notify(vma, addr, > + referenced |= ptep_clear_young_notify(vma, addr, > pvmw.pte); > } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { > - referenced = pmdp_clear_young_notify(vma, addr, > + referenced |= pmdp_clear_young_notify(vma, addr, > pvmw.pmd); > } else { > /* unexpected pmd-mapped page? */