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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CD925C433F5 for ; Thu, 11 Nov 2021 08:29:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B268B6109D for ; Thu, 11 Nov 2021 08:29:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232489AbhKKIcR (ORCPT ); Thu, 11 Nov 2021 03:32:17 -0500 Received: from out30-57.freemail.mail.aliyun.com ([115.124.30.57]:35886 "EHLO out30-57.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231675AbhKKIcP (ORCPT ); Thu, 11 Nov 2021 03:32:15 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R121e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=xhao@linux.alibaba.com;NM=1;PH=DS;RN=5;SR=0;TI=SMTPD_---0Uw0LiUY_1636619363; Received: from B-X3VXMD6M-2058.local(mailfrom:xhao@linux.alibaba.com fp:SMTPD_---0Uw0LiUY_1636619363) by smtp.aliyun-inc.com(127.0.0.1); Thu, 11 Nov 2021 16:29:24 +0800 From: Xin Hao Reply-To: xhao@linux.alibaba.com Subject: Re: [PATCH V1 2/2] mm/damon: Add 'age' of region tracepoint support To: SeongJae Park Cc: sjpark@amazon.de, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20211111082034.13323-1-sj@kernel.org> Message-ID: <929062d1-7e6f-4426-9ffc-b5d2b124f1ad@linux.alibaba.com> Date: Thu, 11 Nov 2021 16:29:23 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: <20211111082034.13323-1-sj@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Park: On 2021/11/11 下午4:20, SeongJae Park wrote: > On Thu, 11 Nov 2021 10:04:38 +0800 Xin Hao wrote: > >> [-- Attachment #1: Type: text/plain, Size: 8070 bytes --] >> >> Hi Park: >> >> On 2021/11/10 下午9:16, SeongJae Park wrote: >>> On Wed, 10 Nov 2021 20:13:14 +0800 Xin Hao wrote: >>> >>>> In patch "mm/damon: add a tracepoint", it adds a >>>> tracepoint for DAMON, it can monitor each region >>>> for each aggregation interval, Now the region add >>>> a new 'age' variable, some primitive would calculate >>>> the priority of each region as a weight, there put it >>>> into tracepoint, so we can easily track the change of >>>> its value through perf or damon-tools. >>> DAMON calculates the age using the address range and nr_accesses of the region, >>> which are already in the tracepoint. In other words, user space can calculate >>> the age on their own. Therefore I thought putting age in the tracepoint as >>> adding unnecessary information, at the moment of the implementation. >>> >>> Of course, I would missing some use cases that need this information in the >>> tracepoint. Furthermore, adding just one more value in the tracepoint wouldn't >>> incur a real issue. But, I'd like to know why this is necessary and how much >>> benefit it provides. Xin, could you please share that? >> I think these two variables nr_access & age have different meanings, >> the nr_access only reflect the >> >> period of sample_interval, We may be able to get the change of age >> through continuous long-term sampling, >> >> But I think this is not very convenient. >> >> We only need to observe the change of age value a small number of times >> to replace the continue sampling of the region. >> >> For example, age has been increasing to 141, but nr_access shows a value >> of 0 at a certain time. Through this，we can >> >> conclude that the region has a very low nr_access value for a long time. > I understand that you don't want to record all the traces and then process the > huge trace data in user space in order to get the age information, because you > want to save disk space and CPU cycles. Is that correct? If so, I think that > makes sense, and it would be better to put that in the commit message. Yes, What you said is absolutely correct, that's how I thought about it, I will add this part of the information to the commit，thanks! > > > Thanks, > SJ > > [...] -- Best Regards! Xin Hao