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=unavailable 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 56AF6ECE58C for ; Fri, 11 Oct 2019 08:39:25 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 259292196E for ; Fri, 11 Oct 2019 08:39:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 259292196E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id A6F288E0005; Fri, 11 Oct 2019 04:39:24 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A1EE28E0001; Fri, 11 Oct 2019 04:39:24 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9350F8E0005; Fri, 11 Oct 2019 04:39:24 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0225.hostedemail.com [216.40.44.225]) by kanga.kvack.org (Postfix) with ESMTP id 6C7A08E0001 for ; Fri, 11 Oct 2019 04:39:24 -0400 (EDT) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id E5BBA180AD806 for ; Fri, 11 Oct 2019 08:39:23 +0000 (UTC) X-FDA: 76030854606.07.farm19_17c3b3bd8b621 X-HE-Tag: farm19_17c3b3bd8b621 X-Filterd-Recvd-Size: 5588 Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by imf15.hostedemail.com (Postfix) with ESMTP for ; Fri, 11 Oct 2019 08:39:23 +0000 (UTC) X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 11 Oct 2019 01:39:21 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.67,283,1566889200"; d="scan'208";a="224268506" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by fmsmga002.fm.intel.com with ESMTP; 11 Oct 2019 01:39:19 -0700 Date: Fri, 11 Oct 2019 16:39:03 +0800 From: Wei Yang To: Konstantin Khlebnikov Cc: Wei Yang , akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, jglisse@redhat.com, mike.kravetz@oracle.com, riel@surriel.com, cai@lca.pw, shakeelb@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [Patch v4 1/2] mm/rmap.c: don't reuse anon_vma if we just want a copy Message-ID: <20191011083903.GB17297@richard> Reply-To: Wei Yang References: <20191011072256.16275-1-richardw.yang@linux.intel.com> <77fb8811-2c95-55d2-de90-7e9ce01267a1@yandex-team.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <77fb8811-2c95-55d2-de90-7e9ce01267a1@yandex-team.ru> User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Oct 11, 2019 at 11:04:16AM +0300, Konstantin Khlebnikov wrote: >On 11/10/2019 10.22, Wei Yang wrote: >> Before commit 7a3ef208e662 ("mm: prevent endless growth of anon_vma >> hierarchy"), anon_vma_clone() doesn't change dst->anon_vma. While after >> this commit, anon_vma_clone() will try to reuse an exist one on forking. >> >> But this commit go a little bit further for the case not forking. >> anon_vma_clone() is called from __vma_split(), __split_vma(), copy_vma() >> and anon_vma_fork(). For the first three places, the purpose here is get >> a copy of src and we don't expect to touch dst->anon_vma even it is >> NULL. While after that commit, it is possible to reuse an anon_vma when >> dst->anon_vma is NULL. This is not we intend to have. >> >> This patch stop reuse anon_vma for non-fork cases. >> >> Fix commit 7a3ef208e662 ("mm: prevent endless growth of anon_vma >> hierarchy") >> >> Signed-off-by: Wei Yang > >Yes, reusing heuristic was designed for fork. >But this isn't strictly necessary - any vmas could share anon_vma. >For example all vmas in system could be linked with single anon_vma. Yes, agree with you. Thanks for your comment :-) > >Acked-by: Konstantin Khlebnikov > >> >> --- >> v4: >> * check dst->anon_vma in each iteration >> v3: >> * use dst->anon_vma and src->anon_vma to get reuse state >> pointed by Konstantin Khlebnikov >> --- >> mm/rmap.c | 24 +++++++++++++++--------- >> 1 file changed, 15 insertions(+), 9 deletions(-) >> >> diff --git a/mm/rmap.c b/mm/rmap.c >> index d9a23bb773bf..c34414567474 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -250,13 +250,19 @@ static inline void unlock_anon_vma_root(struct anon_vma *root) >> * Attach the anon_vmas from src to dst. >> * Returns 0 on success, -ENOMEM on failure. >> * >> - * If dst->anon_vma is NULL this function tries to find and reuse existing >> - * anon_vma which has no vmas and only one child anon_vma. This prevents >> - * degradation of anon_vma hierarchy to endless linear chain in case of >> - * constantly forking task. On the other hand, an anon_vma with more than one >> - * child isn't reused even if there was no alive vma, thus rmap walker has a >> - * good chance of avoiding scanning the whole hierarchy when it searches where >> - * page is mapped. >> + * anon_vma_clone() is called by __vma_split(), __split_vma(), copy_vma() and >> + * anon_vma_fork(). The first three want an exact copy of src, while the last >> + * one, anon_vma_fork(), may try to reuse an existing anon_vma to prevent >> + * endless growth of anon_vma. Since dst->anon_vma is set to NULL before call, >> + * we can identify this case by checking (!dst->anon_vma && src->anon_vma). >> + * >> + * If (!dst->anon_vma && src->anon_vma) is true, this function tries to find >> + * and reuse existing anon_vma which has no vmas and only one child anon_vma. >> + * This prevents degradation of anon_vma hierarchy to endless linear chain in >> + * case of constantly forking task. On the other hand, an anon_vma with more >> + * than one child isn't reused even if there was no alive vma, thus rmap >> + * walker has a good chance of avoiding scanning the whole hierarchy when it >> + * searches where page is mapped. >> */ >> int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src) >> { >> @@ -286,8 +292,8 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src) >> * will always reuse it. Root anon_vma is never reused: >> * it has self-parent reference and at least one child. >> */ >> - if (!dst->anon_vma && anon_vma != src->anon_vma && >> - anon_vma->degree < 2) >> + if (!dst->anon_vma && src->anon_vma && >> + anon_vma != src->anon_vma && anon_vma->degree < 2) >> dst->anon_vma = anon_vma; >> } >> if (dst->anon_vma) >> -- Wei Yang Help you, Help me