From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752375AbeBITOo (ORCPT ); Fri, 9 Feb 2018 14:14:44 -0500 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:43413 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751004AbeBITOn (ORCPT ); Fri, 9 Feb 2018 14:14:43 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R191e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01355;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0SxxE4Jy_1518203671; Subject: Re: [PATCH] mm: thp: fix potential clearing to referenced flag in page_idle_clear_pte_refs_one() To: "Kirill A. Shutemov" Cc: Andrew Morton , 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> <20180209081638.hcmruhckeu47kibx@node.shutemov.name> From: Yang Shi Message-ID: Date: Fri, 9 Feb 2018 11:14:29 -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: <20180209081638.hcmruhckeu47kibx@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 2/9/18 12:16 AM, Kirill A. Shutemov wrote: > On Thu, Feb 08, 2018 at 08:47:35PM -0800, Yang Shi wrote: >> >> 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. > Note, it should be ||=, not |= (although it would work correctly too). checkpatch doesn't like "||=", it reports no space error. Use referenced = referenced || ptep_clear_young_notify(...) to make checkpatch happy. Regards, Yang > > I should really wake up properly before touching code. :-/ >