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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7BB1C7EE23 for ; Wed, 1 Mar 2023 05:19:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229527AbjCAFT2 (ORCPT ); Wed, 1 Mar 2023 00:19:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49258 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229437AbjCAFT1 (ORCPT ); Wed, 1 Mar 2023 00:19:27 -0500 Received: from out30-131.freemail.mail.aliyun.com (out30-131.freemail.mail.aliyun.com [115.124.30.131]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7266C113C7; Tue, 28 Feb 2023 21:19:25 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046060;MF=hsiangkao@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0Vcnk2Ym_1677647960; Received: from 30.97.48.239(mailfrom:hsiangkao@linux.alibaba.com fp:SMTPD_---0Vcnk2Ym_1677647960) by smtp.aliyun-inc.com; Wed, 01 Mar 2023 13:19:21 +0800 Message-ID: <565f2ceb-6e6b-8775-4446-5aefcd377e7d@linux.alibaba.com> Date: Wed, 1 Mar 2023 13:19:19 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [LSF/MM/BPF TOPIC] Cloud storage optimizations From: Gao Xiang To: Matthew Wilcox Cc: Theodore Ts'o , lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org References: <49b6d3de-e5c7-73fc-fa43-5c068426619b@linux.alibaba.com> In-Reply-To: <49b6d3de-e5c7-73fc-fa43-5c068426619b@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 2023/3/1 13:09, Gao Xiang wrote: > > > On 2023/3/1 13:01, Matthew Wilcox wrote: >> On Wed, Mar 01, 2023 at 12:49:10PM +0800, Gao Xiang wrote: >>>> The only problem is that the readahead code doesn't tell the filesystem >>>> whether the request is sync or async.  This should be a simple matter >>>> of adding a new 'bool async' to the readahead_control and then setting >>>> REQ_RAHEAD based on that, rather than on whether the request came in >>>> through readahead() or read_folio() (eg see mpage_readahead()). >>> >>> Great!  In addition to that, just (somewhat) off topic, if we have a >>> "bool async" now, I think it will immediately have some users (such as >>> EROFS), since we'd like to do post-processing (such as decompression) >>> immediately in the same context with sync readahead (due to missing >>> pages) and leave it to another kworker for async readahead (I think >>> it's almost same for decryption and verification). >>> >>> So "bool async" is quite useful on my side if it could be possible >>> passed to fs side.  I'd like to raise my hands to have it. >> >> That's a really interesting use-case; thanks for bringing it up. >> >> Ideally, we'd have the waiting task do the >> decompression/decryption/verification for proper accounting of CPU. >> Unfortunately, if the folio isn't uptodate, the task doesn't even hold >> a reference to the folio while it waits, so there's no way to wake the >> task and let it know that it has work to do.  At least not at the moment >> ... let me think about that a bit (and if you see a way to do it, feel >> free to propose it) > > Honestly, I'd like to take the folio lock until all post-processing is > done and make it uptodate and unlock so that only we need is to pass > locked-folios requests to kworkers for async way or sync handling in > the original context. > > If we unlocked these folios in advance without uptodate, which means > we have to lock it again (which could have more lock contention) and > need to have a way to trace I/Oed but not post-processed stuff in > addition to no I/Oed stuff. I'm not sure which way is better to proper accounting of CPU, but I think individual fs could know more than mm about post-processing handling, I think just have some accounting apis to fses for these. currently I think core-MM just needs to export "async" bool to rac. and EROFS now just do sync decompression for <= 4 pages in z_erofs_readahead(), and I think it can be done better, see: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/erofs/zdata.c?h=v6.2#n832 Thanks, Gao Xiang > > Thanks, > Gao Xiang