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Fri, 01 Jul 2022 07:38:08 -0700 (PDT) Message-ID: Date: Fri, 1 Jul 2022 08:38:07 -0600 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Subject: Re: [PATCH v7 15/15] xfs: Add async buffered write support Content-Language: en-US From: Jens Axboe To: Al Viro , Stefan Roesch Cc: io-uring@vger.kernel.org, kernel-team@fb.com, linux-mm@kvack.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, david@fromorbit.com, jack@suse.cz, hch@infradead.org, Christoph Hellwig References: <20220601210141.3773402-1-shr@fb.com> <20220601210141.3773402-16-shr@fb.com> <0a75a0c4-e2e5-b403-27bc-e43872fecdc1@kernel.dk> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1656686290; a=rsa-sha256; cv=none; b=kKNCG9gi2DUYv0t2vQkTbNLNUn3ycaEJcNYkQ3A0AAKdw7KSgYEU7BxIBCDldSsW6VTnEF egZmokv9bUcA2oeCpg8RWTxqHBAa52q/FwJsUxCfjTylp8nUe6T0ZO9gyRtguePrNRtfy3 eLtlFmqBKXkYAAMhfKzl5dFC+cx/Dj4= ARC-Authentication-Results: i=1; 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dmarc=none; spf=pass (imf01.hostedemail.com: domain of axboe@kernel.dk designates 209.85.215.173 as permitted sender) smtp.mailfrom=axboe@kernel.dk X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1656686290-780205 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 7/1/22 8:30 AM, Jens Axboe wrote: > On 7/1/22 8:19 AM, Jens Axboe wrote: >> On 6/30/22 10:39 PM, Al Viro wrote: >>> On Wed, Jun 01, 2022 at 02:01:41PM -0700, Stefan Roesch wrote: >>>> This adds the async buffered write support to XFS. For async buffered >>>> write requests, the request will return -EAGAIN if the ilock cannot be >>>> obtained immediately. >>> >>> breaks generic/471... >> >> That test case is odd, because it makes some weird assumptions about >> what RWF_NOWAIT means. Most notably that it makes it mean if we should >> instantiate blocks or not. Where did those assumed semantics come from? >> On the read side, we have clearly documented that it should "not wait >> for data which is not immediately available". >> >> Now it is possible that we're returning a spurious -EAGAIN here when we >> should not be. And that would be a bug imho. I'll dig in and see what's >> going on. > > This is the timestamp update that needs doing which will now return > -EAGAIN if IOCB_NOWAIT is set as it may block. > > I do wonder if we should just allow inode time updates with IOCB_NOWAIT, > even on the io_uring side. Either that, or passed in RWF_NOWAIT > semantics don't map completely to internal IOCB_NOWAIT semantics. At > least in terms of what generic/471 is doing, but I'm not sure who came > up with that and if it's established semantics or just some made up ones > from whomever wrote that test. I don't think they make any sense, to be > honest. Further support that generic/471 is just randomly made up semantics, it needs to special case btrfs with nocow or you'd get -EAGAIN anyway for that test. And it's relying on some random timing to see if this works. I really think that test case is just hot garbage, and doesn't test anything meaningful. -- Jens Axboe