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Fri, 05 Jun 2020 15:49:27 -0700 (PDT) Subject: Re: [PATCHSET v5 0/12] Add support for async buffered reads To: Andres Freund Cc: io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org References: <20200526195123.29053-1-axboe@kernel.dk> <20200604005916.niy2mejjcsx4sv6t@alap3.anarazel.de> <6eeff14f-befc-a5cc-08da-cb77f811fbdf@kernel.dk> <20200605202028.d57nklzpeolukni7@alap3.anarazel.de> <20200605203613.ogfilu2edcsfpme4@alap3.anarazel.de> <75bfe993-008d-71ce-7637-369f130bd984@kernel.dk> <3539a454-5321-0bdc-b59c-06f60cc64b56@kernel.dk> <34aadc75-5b8a-331e-e149-45e1547b543e@kernel.dk> <20200605223044.tnh7qsox7zg5uk53@alap3.anarazel.de> <20200605223635.6xesl7u4lxszvico@alap3.anarazel.de> From: Jens Axboe Message-ID: <0e5b7a2d-eb0e-16e6-cc9f-c2ca5fe8cb92@kernel.dk> Date: Fri, 5 Jun 2020 16:49:24 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200605223635.6xesl7u4lxszvico@alap3.anarazel.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 31AC4180559F5 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 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 6/5/20 4:36 PM, Andres Freund wrote: > Hi, > > On 2020-06-05 15:30:44 -0700, Andres Freund wrote: >> On 2020-06-05 15:21:34 -0600, Jens Axboe wrote: >>>>> I can reproduce this, and I see what it is. I'll send out a patch soonish. >>>> >>>> Thinko, can you try with this on top? >>> >>> Sorry that was incomplete, please use this one! >> >> That seems to fix it! Yay. >> >> >> Bulk buffered reads somehow don't quite seem to be performing that well >> though, looking into it. Could be on the pg side too. > > While looking into that, I played with setting > /sys//queue/read_ahead_kb to 0 and noticed that seems to result in > all/most IO done in workers. Is that to be expected? Yes that's expected, if we have to fallback to ->readpage(), then it'll go to a worker. read-ahead is what drives the async nature of it, as we issue the range (plus more, depending on RA window) as read-ahead for the normal read, then wait for it. -- Jens Axboe