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=-7.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS 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 B9524C04EB8 for ; Wed, 12 Dec 2018 13:51:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 70CB82086D for ; Wed, 12 Dec 2018 13:51:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="a44j1xTm" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 70CB82086D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.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 S1727651AbeLLNvw (ORCPT ); Wed, 12 Dec 2018 08:51:52 -0500 Received: from mail-it1-f196.google.com ([209.85.166.196]:33817 "EHLO mail-it1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726232AbeLLNvv (ORCPT ); Wed, 12 Dec 2018 08:51:51 -0500 Received: by mail-it1-f196.google.com with SMTP id x124so13704997itd.1 for ; Wed, 12 Dec 2018 05:51:50 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=eEpCoLPa3YrSbQPOUuLkkfExo2IQG3MVLYpYKqVQQqM=; b=a44j1xTm7+YjGmVQhZtdjl9niRXGEJI+zMU95jJC3GQmKGbT5qr9vit3NMMUnb4ybW ea14xlejYn5Bs/vD3Shmjl+4CoBJyYJ2p9bVmrZq/M8kCwn4fApbRqD3++mUo3cr6W4h sARjkfLFDoS28YPoITsKGmyeXIpjfzGjayx2y3Pby0xGmVcmN91Tsi5rcXoJ51TpVDSV 7OlKQKoW0331ULhS2UiwAwzxPSCyS7Cnus0qCfMPV0dW+L5RUzTl/4jU0fPDbbsFGOLl pPNZ0iO486y0ni0FwqCD0pL5ZxqmYTQrbB3Xcz/zihlZiRHA5BiioUD6G2CbLCD4hlhN Me9A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=eEpCoLPa3YrSbQPOUuLkkfExo2IQG3MVLYpYKqVQQqM=; b=nwal2r9DR+B7ZcpufJRhN6Bis7w66pn2pVf7M01+RCyJZ84TLNvZmKffZ8AFX9aivu z43fvpNzTUCaHIhU2i1LJWslOKsCi2EfEvRGKY+m/R+qplS8RYu6ZtdrcMjQRyKEfnzD gEyDVuKlD0SFrec/wc2RZwP1DNshT0LEajCQqLOE22cbidE5zxdt3Hipi24m03g9bqcQ /i1gJVbUF3fZN47XWPXbNs++9hoqttlC2jYCP0FuYwOENBwPYYUmZyZWiOCerhQCFHrY 6Ai2DX80optIOQW6CUZ/kRH4FWS/qOvXMjHpDgyhu+s9adNyCxcFu4xuOkeEcIOpca/z /7/w== X-Gm-Message-State: AA+aEWaKcwwWlIcCCuVlrdSGX0+QHHOdSe88W5koa/fMKfbD5s6R3tn1 taIly7Kht39DBbu7/UAzj4trOi8U61xjc4FvoH4= X-Google-Smtp-Source: AFSGD/WlNraaJDU+iXTm5iViDyyO+yy39mZAwN6litQXFGstWtT/pRP+KWKwJUbcHqKvyJRMgdoI/DB70YyeNRg1/E0= X-Received: by 2002:a24:a08a:: with SMTP id o132mr6095554ite.1.1544622710375; Wed, 12 Dec 2018 05:51:50 -0800 (PST) MIME-Version: 1.0 References: <20181211051254.16633-1-peterx@redhat.com> <1fc103f7-3164-007d-bcfd-7ad7c60bb6ec@yandex-team.ru> <20181212051540.GA8970@xz-x1> In-Reply-To: <20181212051540.GA8970@xz-x1> From: Konstantin Khlebnikov Date: Wed, 12 Dec 2018 16:51:38 +0300 Message-ID: Subject: Re: [PATCH v2] mm: thp: fix flags for pmd migration when split To: peterx@redhat.com 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 Content-Type: text/plain; charset="UTF-8" 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 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. > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index f2d19e4fe854..aebade83cec9 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2145,23 +2145,25 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > */ > old_pmd = pmdp_invalidate(vma, haddr, pmd); > > -#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION > pmd_migration = is_pmd_migration_entry(old_pmd); > - if (pmd_migration) { > + if (unlikely(pmd_migration)) { > swp_entry_t entry; > > entry = pmd_to_swp_entry(old_pmd); > page = pfn_to_page(swp_offset(entry)); > - } else > -#endif > + write = is_write_migration_entry(entry); > + young = false; > + soft_dirty = pmd_swp_soft_dirty(old_pmd); > + } else { > 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. > > Thanks, > > -- > Peter Xu >