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Thu, 07 Sep 2023 17:30:21 -0700 (PDT) Received: from [192.168.8.100] ([148.252.141.16]) by smtp.gmail.com with ESMTPSA id lz24-20020a170906fb1800b009932337747esm280974ejb.86.2023.09.07.17.30.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 Sep 2023 17:30:21 -0700 (PDT) Message-ID: <6489b8cb-7d54-1e29-f192-a3449ed87fa1@gmail.com> Date: Fri, 8 Sep 2023 01:29:55 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 07/11] vfs: add nowait parameter for file_accessed() To: Dave Chinner , Hao Xu Cc: Matthew Wilcox , io-uring@vger.kernel.org, Jens Axboe , Dominique Martinet , Christian Brauner , Alexander Viro , Stefan Roesch , Clay Harris , "Darrick J . Wong" , linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-cachefs@redhat.com, ecryptfs@vger.kernel.org, linux-nfs@vger.kernel.org, linux-unionfs@vger.kernel.org, bpf@vger.kernel.org, netdev@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-btrfs@vger.kernel.org, codalist@coda.cs.cmu.edu, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, linux-mm@kvack.org, linux-nilfs@vger.kernel.org, devel@lists.orangefs.org, linux-cifs@vger.kernel.org, samba-technical@lists.samba.org, linux-mtd@lists.infradead.org, Wanpeng Li References: <20230827132835.1373581-1-hao.xu@linux.dev> <20230827132835.1373581-8-hao.xu@linux.dev> <642de4e6-801d-fcad-a7ce-bfc6dec3b6e5@linux.dev> Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 31BB21C0029 X-Rspam-User: X-Stat-Signature: ozhafey5ebq8zrcs9ji6ecrisaaznf9b X-Rspamd-Server: rspam03 X-HE-Tag: 1694133022-30045 X-HE-Meta: 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 bNyIpsDD 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 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: On 9/3/23 23:30, Dave Chinner wrote: > On Wed, Aug 30, 2023 at 02:11:31PM +0800, Hao Xu wrote: >> On 8/29/23 19:53, Matthew Wilcox wrote: >>> On Tue, Aug 29, 2023 at 03:46:13PM +0800, Hao Xu wrote: >>>> On 8/28/23 05:32, Matthew Wilcox wrote: >>>>> On Sun, Aug 27, 2023 at 09:28:31PM +0800, Hao Xu wrote: >>>>>> From: Hao Xu >>>>>> >>>>>> Add a boolean parameter for file_accessed() to support nowait semantics. >>>>>> Currently it is true only with io_uring as its initial caller. >>>>> >>>>> So why do we need to do this as part of this series? Apparently it >>>>> hasn't caused any problems for filemap_read(). >>>>> >>>> >>>> We need this parameter to indicate if nowait semantics should be enforced in >>>> touch_atime(), There are locks and maybe IOs in it. >>> >>> That's not my point. We currently call file_accessed() and >>> touch_atime() for nowait reads and nowait writes. You haven't done >>> anything to fix those. >>> >>> I suspect you can trim this patchset down significantly by avoiding >>> fixing the file_accessed() problem. And then come back with a later >>> patchset that fixes it for all nowait i/o. Or do a separate prep series >> >> I'm ok to do that. >> >>> first that fixes it for the existing nowait users, and then a second >>> series to do all the directory stuff. >>> >>> I'd do the first thing. Just ignore the problem. Directory atime >>> updates cause I/O so rarely that you can afford to ignore it. Almost >>> everyone uses relatime or nodiratime. >> >> Hi Matthew, >> The previous discussion shows this does cause issues in real >> producations: https://lore.kernel.org/io-uring/2785f009-2ebb-028d-8250-d5f3a30510f0@gmail.com/#:~:text=fwiw%2C%20we%27ve%20just%20recently%20had%20similar%20problems%20with%20io_uring%20read/write >> > > Then separate it out into it's own patch set so we can have a > discussion on the merits of requiring using noatime, relatime or > lazytime for really latency sensitive IO applications. Changing code > is not always the right solution... Separation sounds reasonable, but it can hardly be said that only latency sensitive apps would care about >1s nowait/async submission delays. Presumably, btrfs can improve on that, but it still looks like it's perfectly legit for filesystems do heavy stuff in timestamping like waiting for IO. Right? -- Pavel Begunkov