From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751341AbeBIIQn (ORCPT ); Fri, 9 Feb 2018 03:16:43 -0500 Received: from mail-wm0-f49.google.com ([74.125.82.49]:36288 "EHLO mail-wm0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751239AbeBIIQm (ORCPT ); Fri, 9 Feb 2018 03:16:42 -0500 X-Google-Smtp-Source: AH8x226CPvPMc39sJaZrtTG73Cb6c9kQ6Jg3Pk7Vp4dbvXBGugqDSvFyg6MuqEf6iQdos32ljBVjzA== Date: Fri, 9 Feb 2018 11:16:38 +0300 From: "Kirill A. Shutemov" To: Yang Shi Cc: Andrew Morton , 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: <20180209081638.hcmruhckeu47kibx@node.shutemov.name> References: <1517875596-76350-1-git-send-email-yang.shi@linux.alibaba.com> <20180208143926.5484e8fd75a56ff35b778bcc@linux-foundation.org> <20180209043325.l6b6hwgeomqldeb6@node.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 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). I should really wake up properly before touching code. :-/ -- Kirill A. Shutemov From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id 5B94A6B0005 for ; Fri, 9 Feb 2018 03:16:43 -0500 (EST) Received: by mail-wm0-f71.google.com with SMTP id g16so3343428wmg.6 for ; Fri, 09 Feb 2018 00:16:43 -0800 (PST) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id c7sor973238edi.12.2018.02.09.00.16.41 for (Google Transport Security); Fri, 09 Feb 2018 00:16:41 -0800 (PST) Date: Fri, 9 Feb 2018 11:16:38 +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: <20180209081638.hcmruhckeu47kibx@node.shutemov.name> References: <1517875596-76350-1-git-send-email-yang.shi@linux.alibaba.com> <20180208143926.5484e8fd75a56ff35b778bcc@linux-foundation.org> <20180209043325.l6b6hwgeomqldeb6@node.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Yang Shi Cc: Andrew Morton , 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 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). I should really wake up properly before touching code. :-/ -- 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