From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CB982C432C0 for ; Thu, 21 Nov 2019 01:07:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A6FFE20715 for ; Thu, 21 Nov 2019 01:07:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726909AbfKUBHv (ORCPT ); Wed, 20 Nov 2019 20:07:51 -0500 Received: from mga06.intel.com ([134.134.136.31]:61555 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726333AbfKUBHv (ORCPT ); Wed, 20 Nov 2019 20:07:51 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 20 Nov 2019 17:07:50 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,223,1571727600"; d="scan'208";a="209930142" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by orsmga006.jf.intel.com with ESMTP; 20 Nov 2019 17:07:48 -0800 Date: Thu, 21 Nov 2019 09:07:39 +0800 From: Wei Yang To: David Hildenbrand Cc: Wei Yang , n-horiguchi@ah.jp.nec.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, James Morse Subject: Re: [PATCH 1/2] mm/memory-failure.c: PageHuge is handled at the beginning of memory_failure Message-ID: <20191121010739.GB12975@richard> Reply-To: Wei Yang References: <20191118082003.26240-1-richardw.yang@linux.intel.com> <1e61c115-5787-9ef4-a449-2e490c53fca7@redhat.com> <20191120004620.GB11061@richard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 20, 2019 at 04:04:44PM +0100, David Hildenbrand wrote: >On 20.11.19 01:46, Wei Yang wrote: >> On Tue, Nov 19, 2019 at 01:23:54PM +0100, David Hildenbrand wrote: >> > On 18.11.19 09:20, Wei Yang wrote: >> > > PageHuge is handled by memory_failure_hugetlb(), so this case could be >> > > removed. >> > > >> > > Signed-off-by: Wei Yang >> > > --- >> > > mm/memory-failure.c | 5 +---- >> > > 1 file changed, 1 insertion(+), 4 deletions(-) >> > > >> > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c >> > > index 3151c87dff73..392ac277b17d 100644 >> > > --- a/mm/memory-failure.c >> > > +++ b/mm/memory-failure.c >> > > @@ -1359,10 +1359,7 @@ int memory_failure(unsigned long pfn, int flags) >> > > * page_remove_rmap() in try_to_unmap_one(). So to determine page status >> > > * correctly, we save a copy of the page flags at this time. >> > > */ >> > > - if (PageHuge(p)) >> > > - page_flags = hpage->flags; >> > > - else >> > > - page_flags = p->flags; >> > > + page_flags = p->flags; >> > > /* >> > > * unpoison always clear PG_hwpoison inside page lock >> > > >> > >> > I somewhat miss a proper explanation why this is safe to do. We access page >> > flags here, so why is it safe to refer to the ones of the sub-page? >> > >> >> Hi, David >> >> I think your comment is on this line: >> >> page_flags = p->flags; >> >> Maybe we need to use this: >> >> page_flags = hpage->flags; >> >> And use hpage in the following or even the whole function? >> >> While one thing interesting is not all "compound page" is PageCompound. For >> some sub-page, we can't get the correct head. This means we may just check on >> the sub-page. > >Oh wait, I think I missed the check right at the beginning of this function, >sorry :/ > >Sooo, memory_failure_hugetlb() was introduced by > >commit 761ad8d7c7b5485bb66fd5bccb58a891fe784544 >Author: Naoya Horiguchi >Date: Mon Jul 10 15:47:47 2017 -0700 > > mm: hwpoison: introduce memory_failure_hugetlb() > >and essentially ripped out all PageHuge() checks *except* this check. This >check was introduced in > >commit 7258ae5c5a2ce2f5969e8b18b881be40ab55433d >Author: James Morse >Date: Fri Jun 16 14:02:29 2017 -0700 > > mm/memory-failure.c: use compound_head() flags for huge pages > > >Maybe that was just a merge oddity as both commits are only ~1month apart. >IOW, I think Naoya's patch forgot to rip it out. > > >Can we make this clear in the patch description like "This is dead code that >cannot be reached after commit 761ad8d7c7b5 ("mm: hwpoison: introduce >memory_failure_hugetlb()")" > >I assume Andrew can fix up when applying > That's very helpful. Thanks for your time sincerely. >Reviewed-by: David Hildenbrand > >-- > >Thanks, > >David / dhildenb -- Wei Yang Help you, Help me