From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id 465176B0007 for ; Thu, 8 Feb 2018 23:47:52 -0500 (EST) Received: by mail-pg0-f69.google.com with SMTP id o11so3082703pgp.14 for ; Thu, 08 Feb 2018 20:47:52 -0800 (PST) Received: from out30-130.freemail.mail.aliyun.com (out30-130.freemail.mail.aliyun.com. [115.124.30.130]) by mx.google.com with ESMTPS id w9-v6si1059820plq.598.2018.02.08.20.47.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 08 Feb 2018 20:47:51 -0800 (PST) Subject: Re: [PATCH] mm: thp: fix potential clearing to referenced flag in page_idle_clear_pte_refs_one() 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 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: owner-linux-mm@kvack.org List-ID: 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 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? */ -- 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