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Sat, 17 Oct 2020 10:30:48 -0700 (PDT) Subject: Re: [PATCH] mm: mark async iocb read as NOWAIT once some data has been, copied To: Matthew Wilcox Cc: linux-mm , Andrew Morton , Johannes Weiner , Kent Overstreet References: <59eae433-9b30-f094-534d-eb5cf0a40a80@kernel.dk> <20201017162820.GI20115@casper.infradead.org> From: Jens Axboe Message-ID: Date: Sat, 17 Oct 2020 11:30:47 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201017162820.GI20115@casper.infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 10/17/20 10:28 AM, Matthew Wilcox wrote: > On Sat, Oct 17, 2020 at 09:30:59AM -0600, Jens Axboe wrote: >> Once we've copied some data for an iocb that is marked with IOCB_WAITQ, >> we should no longer attempt to async lock a new page. Instead make sure >> we return the copied amount, and let the caller retry, instead of >> returning -EIOCBQUEUED for a new page. >> >> This should only be possible with read-ahead disabled on the below >> device, and multiple threads racing on the same file. Haven't been able >> to reproduce on anything else. > > Wouldn't this do the job just as well? > > @@ -2211,6 +2211,8 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb, > > put_page(page); > written += ret; > + if (iocb->ki_flags & IOCB_WAITQ) > + iocb->ki_flags |= IOCB_NOWAIT; > if (!iov_iter_count(iter)) > goto out; > if (ret < nr) { Indeed, that's cleaner. Let me re-test with that just to be on the safe side, and I'll post a new one. -- Jens Axboe