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=-8.4 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT 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 166C2C67839 for ; Thu, 13 Dec 2018 03:23:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BDEF720811 for ; Thu, 13 Dec 2018 03:23:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BDEF720811 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726691AbeLMDXB (ORCPT ); Wed, 12 Dec 2018 22:23:01 -0500 Received: from mx1.redhat.com ([209.132.183.28]:3596 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726298AbeLMDXB (ORCPT ); Wed, 12 Dec 2018 22:23:01 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2D43E307D840; Thu, 13 Dec 2018 03:23:00 +0000 (UTC) Received: from xz-x1 (dhcp-14-116.nay.redhat.com [10.66.14.116]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8C6D75D70A; Thu, 13 Dec 2018 03:22:54 +0000 (UTC) Date: Thu, 13 Dec 2018 11:22:52 +0800 From: Peter Xu To: Konstantin Khlebnikov Cc: =?utf-8?B?0JrQvtC90YHRgtCw0L3RgtC40L0g0KXQu9C10LHQvdC40LrQvtCy?= , Linux Kernel Mailing List , Andrea Arcangeli , Andrew Morton , "Kirill A. Shutemov" , Matthew Wilcox , Michal Hocko , dave.jiang@intel.com, "Aneesh Kumar K.V" , Souptick Joarder , linux-mm@kvack.org, Zi Yan Subject: Re: [PATCH v2] mm: thp: fix flags for pmd migration when split Message-ID: <20181213032252.GB18268@xz-x1> References: <20181211051254.16633-1-peterx@redhat.com> <1fc103f7-3164-007d-bcfd-7ad7c60bb6ec@yandex-team.ru> <20181212051540.GA8970@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Thu, 13 Dec 2018 03:23:00 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 12, 2018 at 04:51:38PM +0300, Konstantin Khlebnikov wrote: > On Wed, Dec 12, 2018 at 8:15 AM Peter Xu wrote: > > > > On Tue, Dec 11, 2018 at 11:21:44AM +0300, Konstantin Khlebnikov wrote: > > > On 11.12.2018 8:12, Peter Xu wrote: > > > > When splitting a huge migrating PMD, we'll transfer all the existing > > > > PMD bits and apply them again onto the small PTEs. However we are > > > > fetching the bits unconditionally via pmd_soft_dirty(), pmd_write() > > > > or pmd_yound() while actually they don't make sense at all when it's > > > > a migration entry. Fix them up by make it conditional. > > > > > > > > Note that if my understanding is correct about the problem then if > > > > without the patch there is chance to lose some of the dirty bits in > > > > the migrating pmd pages (on x86_64 we're fetching bit 11 which is part > > > > of swap offset instead of bit 2) and it could potentially corrupt the > > > > memory of an userspace program which depends on the dirty bit. > > > > > > > > CC: Andrea Arcangeli > > > > CC: Andrew Morton > > > > CC: "Kirill A. Shutemov" > > > > CC: Matthew Wilcox > > > > CC: Michal Hocko > > > > CC: Dave Jiang > > > > CC: "Aneesh Kumar K.V" > > > > CC: Souptick Joarder > > > > CC: Konstantin Khlebnikov > > > > CC: linux-mm@kvack.org > > > > CC: linux-kernel@vger.kernel.org > > > > Signed-off-by: Peter Xu > > > > --- > > > > v2: > > > > - fix it up for young/write/dirty bits too [Konstantin] > > > > --- > > > > mm/huge_memory.c | 15 ++++++++++----- > > > > 1 file changed, 10 insertions(+), 5 deletions(-) > > > > > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > > > index f2d19e4fe854..b00941b3d342 100644 > > > > --- a/mm/huge_memory.c > > > > +++ b/mm/huge_memory.c > > > > @@ -2157,11 +2157,16 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > > > > page = pmd_page(old_pmd); > > > > VM_BUG_ON_PAGE(!page_count(page), page); > > > > page_ref_add(page, HPAGE_PMD_NR - 1); > > > > - if (pmd_dirty(old_pmd)) > > > > - SetPageDirty(page); > > > > - write = pmd_write(old_pmd); > > > > - young = pmd_young(old_pmd); > > > > - soft_dirty = pmd_soft_dirty(old_pmd); > > > > + if (unlikely(pmd_migration)) { > > > > + soft_dirty = pmd_swp_soft_dirty(old_pmd); > > > > + young = write = false; > > > > + } else { > > > > + if (pmd_dirty(old_pmd)) > > > > + SetPageDirty(page); > > > > + write = pmd_write(old_pmd); > > > > + young = pmd_young(old_pmd); > > > > + soft_dirty = pmd_soft_dirty(old_pmd); > > > > + } > > > > > > Write/read-only is encoded into migration entry. > > > I suppose there should be something like this: > > > > > > --- a/mm/huge_memory.c > > > +++ b/mm/huge_memory.c > > > @@ -2151,16 +2151,21 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > > > > > > entry = pmd_to_swp_entry(old_pmd); > > > page = pfn_to_page(swp_offset(entry)); > > > + write = is_write_migration_entry(entry); > > > + young = false; > > > + soft_dirty = pmd_swp_soft_dirty(old_pmd); > > > } else > > > #endif > > > + { > > > page = pmd_page(old_pmd); > > > + if (pmd_dirty(old_pmd)) > > > + SetPageDirty(page); > > > + write = pmd_write(old_pmd); > > > + young = pmd_young(old_pmd); > > > + soft_dirty = pmd_soft_dirty(old_pmd); > > > + } > > > VM_BUG_ON_PAGE(!page_count(page), page); > > > page_ref_add(page, HPAGE_PMD_NR - 1); > > > - if (pmd_dirty(old_pmd)) > > > - SetPageDirty(page); > > > - write = pmd_write(old_pmd); > > > - young = pmd_young(old_pmd); > > > - soft_dirty = pmd_soft_dirty(old_pmd); > > > > > > /* > > > * Withdraw the table only after we mark the pmd entry invalid. > > > > > > > Oops yes, I missed the write bit. Thanks for pointing it out. > > > > Should I repost with your authorship and your sign-off? > > Feel free to use this piece for your own patch. > > > Or even I'll > > consider to directly drop the CONFIG_ARCH_ENABLE_THP_MIGRATION if with > > that since I don't see much gain to keep it: > > Yep, this ifdef could be removed. > Without CONFIG_ARCH_ENABLE_THP_MIGRATION > is_pmd_migration_entry() is constant 0 so compiler should eliminate "if" branch. Thank you, Konstantin. I'll post v3 with the macro dropped. Regards, -- Peter Xu