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=-5.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT 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 600D8C49EA5 for ; Thu, 24 Jun 2021 17:38:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4316E613E3 for ; Thu, 24 Jun 2021 17:38:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232483AbhFXRlK (ORCPT ); Thu, 24 Jun 2021 13:41:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59444 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229928AbhFXRlH (ORCPT ); Thu, 24 Jun 2021 13:41:07 -0400 Received: from mail-qk1-x730.google.com (mail-qk1-x730.google.com [IPv6:2607:f8b0:4864:20::730]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F1139C061574; Thu, 24 Jun 2021 10:38:46 -0700 (PDT) Received: by mail-qk1-x730.google.com with SMTP id 19so5869836qky.13; Thu, 24 Jun 2021 10:38:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to; bh=USIvcW2GRTbxr6DQIhIcD3oRQUCmqXrjMxJlSlcyZyY=; b=kbR6mQPR3V5N+3juXGRBcBiazil8iZpsxfWzxd9BvUFR3SpS9O350b+QwJv7cVfd6W qmn9n8UtxJAx8JoVnoN7znSebG/jRlB7ZGrQNXz8XtSTx7r4iM/eekYQC1EQLNPcBtkk tA1JBxd4jXacZTtvOSKqLEpkl7Dzjpd8db6iH+n/jL5mrKjORyvQB0dFbRB+M38TtY4S 3L0NcRdwJuMeZ3/gPAwdYCyUt4b+Q6E7JybJHYoWhqxaZ3DKY+BdaxmATNjy8eJ05Xm4 9Ba/QGQ+cmFAcmMN3URpDChlQGHE8gz1WgUGX+I7X1TD9Ba1nTqqJFZSeK43L17Fu8t8 uwgw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to; bh=USIvcW2GRTbxr6DQIhIcD3oRQUCmqXrjMxJlSlcyZyY=; b=I0HuYQVMkWHwP89hSCBcxzGk2ZyfhrP82Gib6gajFxvV1gG0tRIbZZScDOEZGd1TUv mssO5+aVwgx7oGOl47pAOYrFNwDANymmH8RwuHkMuSXQj106eEosqpGPjSVaNaIr3hw7 YvXQLT+gInpBsM7Wi5Piw1wispqACvRBzTHRLlI3tQqqLGPWZPp+NpKie7sYze4JS/SC J4sNey2rA/N304DIoY7YCZ/6DrQ+0qTBfFIwcA6vuPNXTqp9wRyrdqF5F24v8ACcFTuw AFrwTUOml/W69OebsijLTyoyRlJD1K1BWTVX8gVdA8OOBWZPfI02NGxEsBDBO78HJA4D DSwQ== X-Gm-Message-State: AOAM533VZTzxvOrQEG7RwgxkFuTXS81y/R9ChH4j8FgRharItMG+AHMf idNHRF5zSjIOHKDTMGScMtI= X-Google-Smtp-Source: ABdhPJxsAxEekOJRnWG7tLXyRAMmuBFyqd4fVq5FToPvGsrdsQqeT0S7KrBF8UWNZT4FhKuSR1CeKQ== X-Received: by 2002:a37:9d90:: with SMTP id g138mr3040398qke.212.1624556326108; Thu, 24 Jun 2021 10:38:46 -0700 (PDT) Received: from localhost.localdomain (ec2-35-169-212-159.compute-1.amazonaws.com. [35.169.212.159]) by smtp.gmail.com with ESMTPSA id 61sm1110156qtf.37.2021.06.24.10.38.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Jun 2021 10:38:45 -0700 (PDT) From: SeongJae Park X-Google-Original-From: SeongJae Park To: Shakeel Butt Cc: SeongJae Park , acme@kernel.org, alexander.shishkin@linux.intel.com, amit@kernel.org, benh@kernel.crashing.org, Brendan Higgins , Jonathan Corbet , David Hildenbrand , dwmw@amazon.com, Marco Elver , "Du, Fan" , foersleo@amazon.de, greg@kroah.com, Greg Thelen , guoju.fgj@alibaba-inc.com, jgowans@amazon.com, Mel Gorman , mheyne@amazon.de, Minchan Kim , Ingo Molnar , namhyung@kernel.org, "Peter Zijlstra (Intel)" , Rik van Riel , David Rientjes , Steven Rostedt , Mike Rapoport , Shuah Khan , sieberf@amazon.com, snu@zelle79.org, Vlastimil Babka , Vladimir Davydov , zgf574564920@gmail.com, linux-damon@amazon.com, Linux MM , linux-doc@vger.kernel.org, LKML Subject: Re: [PATCH v31 05/13] mm/damon: Implement primitives for the virtual memory address spaces Date: Thu, 24 Jun 2021 17:38:39 +0000 Message-Id: <20210624173839.1766-1-sjpark@amazon.de> X-Mailer: git-send-email 2.17.1 In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: SeongJae Park On Thu, 24 Jun 2021 09:33:07 -0700 Shakeel Butt wrote: > On Thu, Jun 24, 2021 at 8:21 AM SeongJae Park wrote: > > > > From: SeongJae Park > > > > On Thu, 24 Jun 2021 07:42:44 -0700 Shakeel Butt wrote: > > > > > On Thu, Jun 24, 2021 at 3:26 AM SeongJae Park wrote: > > > > > > > [...] > > > > > > +/* > > > > > > + * Get the three regions in the given target (task) > > > > > > + * > > > > > > + * Returns 0 on success, negative error code otherwise. > > > > > > + */ > > > > > > +static int damon_va_three_regions(struct damon_target *t, > > > > > > + struct damon_addr_range regions[3]) > > > > > > +{ > > > > > > + struct mm_struct *mm; > > > > > > + int rc; > > > > > > + > > > > > > + mm = damon_get_mm(t); > > > > > > + if (!mm) > > > > > > + return -EINVAL; > > > > > > + > > > > > > + mmap_read_lock(mm); > > > > > > + rc = __damon_va_three_regions(mm->mmap, regions); > > > > > > + mmap_read_unlock(mm); > > > > > > > > > > This is being called for each target every second by default. Seems > > > > > too aggressive. Applications don't change their address space every > > > > > second. I would recommend to default ctx->primitive_update_interval to > > > > > a higher default value. > > > > > > > > Good point. If there are many targets and each target has a huge number of > > > > VMAs, the overhead could be high. Nevertheless, I couldn't find the overhead > > > > in my test setup. Also, it seems someone are already started exploring DAMON > > > > patchset with the default value. and usages from others. Silently changing the > > > > default value could distract such people. So, if you think it's ok, I'd like > > > > to change the default value only after someone finds the overhead from their > > > > usages and asks a change. > > > > > > > > If you disagree or you found the overhead from your usage, please feel free to > > > > let me know. > > > > > > > > > > mmap lock is a source contention in the real world workloads. We do > > > observe in our fleet and many others (like Facebook) do complain on > > > this issue. This is the whole motivation behind SFP, maple tree and > > > many other mmap lock scalability work. I would be really careful to > > > add another source of contention on mmap lock. Yes, the user can > > > change this interval themselves but we should not burden them with > > > this internal knowledge like "oh if you observe high mmap contention > > > you may want to increase this specific interval". We should set a good > > > default value to avoid such situations (most of the time). > > > > Thank you for this nice clarification. I can understand your concern because I > > also worked for an HTM-based solution of the scalability issue before. > > > > However, I have neither strong preference nor confidence for the new default > > value at the moment. Could you please recommend one if you have? > > > > I would say go with a conservative value like 60 seconds. Though there > is no scientific reason behind this specific number, I think it would > be a good compromise. Applications usually don't change their address > space layout that often. Ok, I will use that from the next spin. Thank you for this nice suggestion. Thanks, SeongJae Park