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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9A6ADCD11DD for ; Thu, 28 Mar 2024 19:36:50 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 301A76B009C; Thu, 28 Mar 2024 15:36:50 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2B2186B009D; Thu, 28 Mar 2024 15:36:50 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 17B006B009E; Thu, 28 Mar 2024 15:36:50 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id EBA1C6B009C for ; Thu, 28 Mar 2024 15:36:49 -0400 (EDT) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id AA169120269 for ; Thu, 28 Mar 2024 19:36:49 +0000 (UTC) X-FDA: 81947455338.24.A3AF5F6 Received: from out-188.mta0.migadu.com (out-188.mta0.migadu.com [91.218.175.188]) by imf06.hostedemail.com (Postfix) with ESMTP id B1490180016 for ; Thu, 28 Mar 2024 19:36:47 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=KOhyPkwf; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf06.hostedemail.com: domain of kent.overstreet@linux.dev designates 91.218.175.188 as permitted sender) smtp.mailfrom=kent.overstreet@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1711654608; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=DJhQSNC8P3FZAcQGH5MKGoCL/i0YWNxW5QJiOdjoIKM=; b=JqUIkmcGyTnrw6rI2DaEY+bpgvJ5pEYWV9sfRdhdk6TUdYvM29bziyWmc25pdZ5MwEF0Q/ Z7d+n0wIEpCq7v0oNlGv+EpQLgmL5vJ+MCjmq5PwOx3FXvXFIqDqOgI5YXCJSdQymZ5Lys YqxoA6drok3eydodz//LRNqTSJ9OA08= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=KOhyPkwf; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf06.hostedemail.com: domain of kent.overstreet@linux.dev designates 91.218.175.188 as permitted sender) smtp.mailfrom=kent.overstreet@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1711654608; a=rsa-sha256; cv=none; b=sK+kaskpBABQm1HbLexQU/4O7JFXsFg6bAn968kgs5UAonS3EsWDf1FPKHhPNoEjG/kzr9 yMY6B5IDYC5cA4KGTEob6S2e/Wke1nsxEWBHNAxSg7dmQN4KhGmOYuVgH/J1YSpKTlgmIS u4Xgcw4ZjQRrwUfnG1lcZzkHG7r4hvE= Date: Thu, 28 Mar 2024 15:36:42 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1711654605; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=DJhQSNC8P3FZAcQGH5MKGoCL/i0YWNxW5QJiOdjoIKM=; b=KOhyPkwfh4AJ36P0Wk23YQd+c5nTMsS/2IeCJZwGRwbyr4H3icT9wa2oQctiIVfamv3ID3 rwogfybHV3A+T2luKtMCILW//22chCuSXNtDsyM+mNsd13FxEYD55966GAPPnHdClx/unU /4uAXkz4S8Vxr2E+UpUEFv8P9ZtTg6k= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Kent Overstreet To: Andrew Morton Cc: Kemeng Shi , willy@infradead.org, jack@suse.cz, bfoster@redhat.com, tj@kernel.org, dsterba@suse.com, mjguzik@gmail.com, dhowells@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v2 0/6] Improve visibility of writeback Message-ID: References: <20240327155751.3536-1-shikemeng@huaweicloud.com> <20240327104010.73d1180fbabe586f9e3f7bd2@linux-foundation.org> <20240328122352.a001a56aed97b01ac5931998@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240328122352.a001a56aed97b01ac5931998@linux-foundation.org> X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: B1490180016 X-Stat-Signature: rqw7n69cmh9gcei6dhffidwzesqubiyr X-HE-Tag: 1711654607-786842 X-HE-Meta: U2FsdGVkX19DjZwzj+dYI9luKEyLR6A5iE4KFvVoZY/4ahV7rsOw9Z+wU5IyKY42m3vj2Ks1Fh8IMNCsvFKbi7Mm1tr4R3uwFInD9yxyOxiXMk11tbYScW1w4utkuVyTpQtPcrfSwzxzoB+toTtTOiRTxiRVXLmwEQtpCzfOS6YkdWOX7ABgK/J7h7ljCcRqAYenxzxfdk5K7ncVWV+x0AK+kqfG4GPnqxQl6mc/9OV+17UPjevfQhx4g8FvLFBbJG/1MSHyrTCQonixTDAD56ydgh7rfNVLc0Kec5BuR0OWT2+lKrxUMOUFXiHPWAkUEfYAabddSZhG04qh++VoonwZaIcxJBlxBTUnzbAF+pVIexFwUtif7VpSkxaivg9FL5CPYq3aoNb3Go0Ttau7Lp85xrgzQjM13x5QKTIlQzArYSSdxUpHxc/uZackijKa0J51fkzw41nNbwjSe2oVcyJ0uUuoHyx4i6w7ZnmLwP9fk27pUGzLc/uiYQM2CU3gpYsLATb9q2LCRYyV3+OphEA0EwTHDtCyReDbKm1Bw/wIdX0rKjT5w/VOrGA1QeYjQ1gCOIqTl+tIGxuz9P4a9NwrIhhx4oN1fgVjSPgGnOCkx+jWY1HskfbYEXYVHAN3R0uBIP6XoLhuODrfGQOfVjcRi86mpJgLWKy5FVs19UeQTBEoHhrNHp5YVoM9elshv4lETA60OCnlW1YMFbtataKSKqFqX1/3/3cqJ4Cz346tkbg3G1Ui1WG3YXoHpsUaIIZaIPanROF5PVEub7WuxRHaDa2WdmKo97jRyft0kz6SajeM1w9yw6UTMG5eeIpi7neUquM0fJWONyvN5quIDH/TAS6WCsyH5gsQZgbfc3BMU914qEs6j99h2uqO3ZxOF/LOFyxineV4MLx2tFzT2fGqHo03lPh4oIZqFfhD3TM29LPfSrffvOCrOwbECQPtuA/ldrm5iBfSbTpjeIZ cM7IXNvO XXfb5YY6jCFHVbgTI3IbOuIUFvVjlcNWHiFmT/GK4dv1C+hz7LRsgbIJP5AYeNEV//qx98mXjI15XzTmu6dBNM+AlBitUrVbKEPyrqw2GeCIhQRQlihxoKztIEtLnbdI74P+lLny4e5HKJsPe4jAolUeulQ== 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: List-Subscribe: List-Unsubscribe: On Thu, Mar 28, 2024 at 12:23:52PM -0700, Andrew Morton wrote: > On Thu, 28 Mar 2024 15:15:03 -0400 Kent Overstreet wrote: > > > On Wed, Mar 27, 2024 at 10:40:10AM -0700, Andrew Morton wrote: > > > On Wed, 27 Mar 2024 23:57:45 +0800 Kemeng Shi wrote: > > > > > > > This series tries to improve visilibity of writeback. > > > > > > Well... why? Is anyone usefully using the existing instrumentation? > > > What is to be gained by expanding it further? What is the case for > > > adding this code? > > > > > > I don't recall hearing of anyone using the existing debug > > > instrumentation so perhaps we should remove it! > > > > Remove debug instrumentation!? Surely you just? > > Absolutely not. Any code in the kernel should have ongoing > justification for remaining there. If no such justification exists, > out it goes. Certainly, but this isn't remotely a case where I'd expect to be getting that kind of feedback. Debugging instrumentation is very much a case where no one notices it 99% of the time, but when you need it you _really_ need it. Not having it can turn a 10 minute "oh, that thing is acting wonky - it's because your system is overloaded/your drive is wonky/x subsystem sucks, we know about it and we're working on it" into a weeklong bughunt, burning up expensive engineer time pointlessly. To debug complex systems efficiently, in production, in the wild, we need to be able to see what's going on - we need more of this stuff. Not to say that this couldn't use more work - perhaps additional focus on what kinds of issues we expect to need to debug with this, what the numbers mean and are useful for, documentation on how this relates to writeback internals, etc.