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=-2.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 DE69FC41514 for ; Tue, 30 Jul 2019 12:39:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AD61720C01 for ; Tue, 30 Jul 2019 12:39:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564490383; bh=5EpHfhYIqzNgNKgwS9X5Ks26Lj4nnAt3gfaDtOoZ5Ag=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=MwDIknba1Tx/5eT9Hm+xguqTa4t4oWuwLLh9u5G8OfBU2ONREkptLN0FpKPb22Mkb U0W0iWpwqYCrVJd2QJC/A3NdTp9i5iuoipDgvjj8yGDAKe6x6+cN1c4eT7+p6NjMWU 8QAB9NM62rmBOROi5ZVgtXdD7HddTMYRhFa8Vve0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730553AbfG3Mjm (ORCPT ); Tue, 30 Jul 2019 08:39:42 -0400 Received: from mail-pg1-f195.google.com ([209.85.215.195]:44226 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729199AbfG3Mjm (ORCPT ); Tue, 30 Jul 2019 08:39:42 -0400 Received: by mail-pg1-f195.google.com with SMTP id i18so30002613pgl.11 for ; Tue, 30 Jul 2019 05:39:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=Ab9+yQllgrxhV1PV/fDiWkVd8KTBl0Z4jc93v/FyaQw=; b=YPayV2Tsa3gOdnqXV9g1d7Z1RXrW8NzdVyVVzOilsA1igzI/rHFmlxWqz2QNxpW4U6 dD5MFPpint7VYr6z8bGMtBS+li8hGGd4Nu1XQkS7keaj6l/7tg/mAyHSxedtcGS9wFw6 9sJgyM95LXS43bfOXzUMz6mCasAm7hzL44R90nb1HLTsJewZ4NcItRMQpRzVNSKcTpb1 58FaOZwjOG0vLlee5mEg2Axr4+CZnXJwJP36yn4oI9ZOOP3a3cOPAi1CPhNv/AQ+E+Gx nbtaK5VP7nEcHtlYX8cu2649N1q2zeVjHVwCVQaPys5UeyUD8TWr/IT8oWKWqYsSyFdJ zK4g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=Ab9+yQllgrxhV1PV/fDiWkVd8KTBl0Z4jc93v/FyaQw=; b=YTVoONryBZdDgLt/R8sTaSFPFsn73cqmVzgdDMaef5iC1mnh7LDuMv9VeV4p+EEI83 Xh+57tR0Nn7qy/D7VpkeQsJyZeaNEJKxOA3gQ8+CiezIniWWtNkqjgPtnkmnOPhmeswe 3tFhy8vZCBPQYt3ANZ43OFszcxSYSh8sabioZADjvLJCuTgFJXNpEA0138y2KRwu2N+4 YKQofsVNKT/LOBcQbinCfLufMyZ5HCdzGXTMJn3cofIx4Urey2oIXLewZEa8TbzMoZgM ZT22JqV4dEiktwX0pJ8e0oGJ45paU7bxYfsDeSS6/gC1+BzlL5t7sWtm6hgIRtw4NjEx Y4tA== X-Gm-Message-State: APjAAAWD+kbXByO9V2nYA9MTa/Y62WWbyg2rJhpayxdYlwX4LCEqriF9 Tw80YRcRofhCM5Ea910/5rvHW7yr X-Google-Smtp-Source: APXvYqyKe+n/nS4aOkmskr/0g93PGfZyD+f/iJDZav+UStfSIraoDl2l/xmMU8fmzTdF6fnjVG6qKQ== X-Received: by 2002:a63:db47:: with SMTP id x7mr108219665pgi.375.1564490381025; Tue, 30 Jul 2019 05:39:41 -0700 (PDT) Received: from google.com ([2401:fa00:d:0:98f1:8b3d:1f37:3e8]) by smtp.gmail.com with ESMTPSA id k70sm64512464pje.14.2019.07.30.05.39.37 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 30 Jul 2019 05:39:39 -0700 (PDT) Date: Tue, 30 Jul 2019 21:39:35 +0900 From: Minchan Kim To: Michal Hocko Cc: Andrew Morton , LKML , linux-mm , Miguel de Dios , Wei Wang , Johannes Weiner , Mel Gorman Subject: Re: [PATCH] mm: release the spinlock on zap_pte_range Message-ID: <20190730123935.GB184615@google.com> References: <20190729071037.241581-1-minchan@kernel.org> <20190729074523.GC9330@dhcp22.suse.cz> <20190729082052.GA258885@google.com> <20190729083515.GD9330@dhcp22.suse.cz> <20190730121110.GA184615@google.com> <20190730123237.GR9330@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190730123237.GR9330@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 30, 2019 at 02:32:37PM +0200, Michal Hocko wrote: > On Tue 30-07-19 21:11:10, Minchan Kim wrote: > > On Mon, Jul 29, 2019 at 10:35:15AM +0200, Michal Hocko wrote: > > > On Mon 29-07-19 17:20:52, Minchan Kim wrote: > > > > On Mon, Jul 29, 2019 at 09:45:23AM +0200, Michal Hocko wrote: > > > > > On Mon 29-07-19 16:10:37, Minchan Kim wrote: > > > > > > In our testing(carmera recording), Miguel and Wei found unmap_page_range > > > > > > takes above 6ms with preemption disabled easily. When I see that, the > > > > > > reason is it holds page table spinlock during entire 512 page operation > > > > > > in a PMD. 6.2ms is never trivial for user experince if RT task couldn't > > > > > > run in the time because it could make frame drop or glitch audio problem. > > > > > > > > > > Where is the time spent during the tear down? 512 pages doesn't sound > > > > > like a lot to tear down. Is it the TLB flushing? > > > > > > > > Miguel confirmed there is no such big latency without mark_page_accessed > > > > in zap_pte_range so I guess it's the contention of LRU lock as well as > > > > heavy activate_page overhead which is not trivial, either. > > > > > > Please give us more details ideally with some numbers. > > > > I had a time to benchmark it via adding some trace_printk hooks between > > pte_offset_map_lock and pte_unmap_unlock in zap_pte_range. The testing > > device is 2018 premium mobile device. > > > > I can get 2ms delay rather easily to release 2M(ie, 512 pages) when the > > task runs on little core even though it doesn't have any IPI and LRU > > lock contention. It's already too heavy. > > > > If I remove activate_page, 35-40% overhead of zap_pte_range is gone > > so most of overhead(about 0.7ms) comes from activate_page via > > mark_page_accessed. Thus, if there are LRU contention, that 0.7ms could > > accumulate up to several ms. > > Thanks for this information. This is something that should be a part of > the changelog. I am sorry to still poke into this because I still do not I will include it. > have a full understanding of what is going on and while I do not object > to drop the spinlock I still suspect this is papering over a deeper > problem. I couldn't come up with better solution. Feel free to suggest it. > > If mark_page_accessed is really expensive then why do we even bother to > do it in the tear down path in the first place? Why don't we simply set > a referenced bit on the page to reflect the young pte bit? I might be > missing something here of course. commit bf3f3bc5e73 Author: Nick Piggin Date: Tue Jan 6 14:38:55 2009 -0800 mm: don't mark_page_accessed in fault path Doing a mark_page_accessed at fault-time, then doing SetPageReferenced at unmap-time if the pte is young has a number of problems. mark_page_accessed is supposed to be roughly the equivalent of a young pte for unmapped references. Unfortunately it doesn't come with any context: after being called, reclaim doesn't know who or why the page was touched. So calling mark_page_accessed not only adds extra lru or PG_referenced manipulations for pages that are already going to have pte_young ptes anyway, but it also adds these references which are difficult to work with from the context of vma specific references (eg. MADV_SEQUENTIAL pte_young may not wish to contribute to the page being referenced). Then, simply doing SetPageReferenced when zapping a pte and finding it is young, is not a really good solution either. SetPageReferenced does not correctly promote the page to the active list for example. So after removing mark_page_accessed from the fault path, several mmap()+touch+munmap() would have a very different result from several read(2) calls for example, which is not really desirable. Signed-off-by: Nick Piggin Acked-by: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds