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=-6.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY, URIBL_BLOCKED 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 C7FFEC43382 for ; Thu, 27 Sep 2018 16:05:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8CFA0216FC for ; Thu, 27 Sep 2018 16:05:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8CFA0216FC Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.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 S1728451AbeI0WYU (ORCPT ); Thu, 27 Sep 2018 18:24:20 -0400 Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:45286 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727541AbeI0WYU (ORCPT ); Thu, 27 Sep 2018 18:24:20 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R231e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04428;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0T9aPzPi_1538064298; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0T9aPzPi_1538064298) by smtp.aliyun-inc.com(127.0.0.1); Fri, 28 Sep 2018 00:05:01 +0800 Subject: Re: [v2 PATCH 1/2 -mm] mm: mremap: dwongrade mmap_sem to read when shrinking To: Vlastimil Babka , mhocko@kernel.org, kirill@shutemov.name, willy@infradead.org, ldufour@linux.vnet.ibm.com, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1537985434-22655-1-git-send-email-yang.shi@linux.alibaba.com> <8c04afa9-45c2-be18-c084-058add73c978@suse.cz> From: Yang Shi Message-ID: <60c0544d-917f-89e1-2806-80c1beb830a0@linux.alibaba.com> Date: Thu, 27 Sep 2018 09:04:55 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <8c04afa9-45c2-be18-c084-058add73c978@suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/27/18 4:50 AM, Vlastimil Babka wrote: > On 9/26/18 8:10 PM, Yang Shi wrote: >> Subject: [v2 PATCH 1/2 -mm] mm: mremap: dwongrade mmap_sem to read > when shrinking > > "downgrade" in the subject Will fix in the next version. Thanks, Yang > >> Other than munmap, mremap might be used to shrink memory mapping too. >> So, it may hold write mmap_sem for long time when shrinking large >> mapping, as what commit ("mm: mmap: zap pages with read mmap_sem in >> munmap") described. >> >> The mremap() will not manipulate vmas anymore after __do_munmap() call for >> the mapping shrink use case, so it is safe to downgrade to read mmap_sem. >> >> So, the same optimization, which downgrades mmap_sem to read for zapping >> pages, is also feasible and reasonable to this case. >> >> The period of holding exclusive mmap_sem for shrinking large mapping >> would be reduced significantly with this optimization. >> >> MREMAP_FIXED and MREMAP_MAYMOVE are more complicated to adopt this >> optimization since they need manipulate vmas after do_munmap(), >> downgrading mmap_sem may create race window. >> >> Simple mapping shrink is the low hanging fruit, and it may cover the >> most cases of unmap with munmap together. >> >> Cc: Michal Hocko >> Cc: Kirill A. Shutemov >> Cc: Matthew Wilcox >> Cc: Laurent Dufour >> Cc: Vlastimil Babka >> Cc: Andrew Morton >> Signed-off-by: Yang Shi > Looks fine, > > Acked-by: Vlastimil Babka > > Nit: > >> --- a/mm/mmap.c >> +++ b/mm/mmap.c >> @@ -2687,8 +2687,8 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma, >> * work. This now handles partial unmappings. >> * Jeremy Fitzhardinge >> */ >> -static int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len, >> - struct list_head *uf, bool downgrade) >> +int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len, >> + struct list_head *uf, bool downgrade) >> { >> unsigned long end; >> struct vm_area_struct *vma, *prev, *last; >> diff --git a/mm/mremap.c b/mm/mremap.c >> index 5c2e185..8f1ec2b 100644 >> --- a/mm/mremap.c >> +++ b/mm/mremap.c >> @@ -525,6 +525,7 @@ static int vma_expandable(struct vm_area_struct *vma, unsigned long delta) >> unsigned long ret = -EINVAL; >> unsigned long charged = 0; >> bool locked = false; >> + bool downgrade = false; > Maybe "downgraded" is more accurate here, or even "downgraded_mmap_sem".