From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752491AbeBIEda (ORCPT ); Thu, 8 Feb 2018 23:33:30 -0500 Received: from mail-wm0-f67.google.com ([74.125.82.67]:51936 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752154AbeBIEd2 (ORCPT ); Thu, 8 Feb 2018 23:33:28 -0500 X-Google-Smtp-Source: AH8x225L1w1adbtzkdvfeIUjhg4rfbbtZqrb9r/y+mnVSi7Pmiieo4iTcUIWt25+irf0Mqv9h66y/w== Date: Fri, 9 Feb 2018 07:33:25 +0300 From: "Kirill A. Shutemov" To: Andrew Morton Cc: Yang Shi , kirill.shutemov@linux.intel.com, gavin.dg@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: thp: fix potential clearing to referenced flag in page_idle_clear_pte_refs_one() Message-ID: <20180209043325.l6b6hwgeomqldeb6@node.shutemov.name> References: <1517875596-76350-1-git-send-email-yang.shi@linux.alibaba.com> <20180208143926.5484e8fd75a56ff35b778bcc@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180208143926.5484e8fd75a56ff35b778bcc@linux-foundation.org> User-Agent: NeoMutt/20171215 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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): 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? */ -- Kirill A. Shutemov From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 887F56B0005 for ; Thu, 8 Feb 2018 23:33:29 -0500 (EST) Received: by mail-wm0-f70.google.com with SMTP id b195so3162051wmb.1 for ; Thu, 08 Feb 2018 20:33:29 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id a67sor809453edf.1.2018.02.08.20.33.28 for (Google Transport Security); Thu, 08 Feb 2018 20:33:28 -0800 (PST) Date: Fri, 9 Feb 2018 07:33:25 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH] mm: thp: fix potential clearing to referenced flag in page_idle_clear_pte_refs_one() Message-ID: <20180209043325.l6b6hwgeomqldeb6@node.shutemov.name> References: <1517875596-76350-1-git-send-email-yang.shi@linux.alibaba.com> <20180208143926.5484e8fd75a56ff35b778bcc@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180208143926.5484e8fd75a56ff35b778bcc@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Yang Shi , kirill.shutemov@linux.intel.com, gavin.dg@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org 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): 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? */ -- Kirill A. Shutemov -- 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