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Sat, 17 Oct 2020 12:13:28 -0700 (PDT) Date: Sat, 17 Oct 2020 15:13:20 -0400 From: Kent Overstreet To: Jens Axboe Cc: Matthew Wilcox , linux-mm , Andrew Morton , Johannes Weiner Subject: Re: [PATCH] mm: mark async iocb read as NOWAIT once some data has been, copied Message-ID: <20201017191320.GA2198928@zaphod.evilpiepirate.org> References: <59eae433-9b30-f094-534d-eb5cf0a40a80@kernel.dk> <20201017162820.GI20115@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Sat, Oct 17, 2020 at 11:30:47AM -0600, Jens Axboe wrote: > 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. generic_file_buffered_read() has written passed in, which can be nonzero (DIO fallback) - we probably want the check to be at the top of the loop.