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Thu, 29 Oct 2020 08:05:07 -0700 (PDT) Subject: Re: + fs-break-generic_file_buffered_read-up-into-multiple-functions.patch added to -mm tree To: Matthew Wilcox Cc: Andrew Morton , linux-mm@kvack.org, kent.overstreet@gmail.com References: <20201025220817.XxXVE%akpm@linux-foundation.org> <20201027133551.GW20115@casper.infradead.org> <20201028152235.125172e46ae70ba4d7094469@linux-foundation.org> <543aa047-f334-cc40-8466-51bff70ac3b3@kernel.dk> <20201029145759.GA27442@casper.infradead.org> <74d36f69-e14e-40e1-531e-edd1d2e3c344@kernel.dk> <20201029150342.GB27442@casper.infradead.org> From: Jens Axboe Message-ID: <73eb7276-f326-c481-4936-6c6c125edfbc@kernel.dk> Date: Thu, 29 Oct 2020 09:05:07 -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: <20201029150342.GB27442@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 10/29/20 9:03 AM, Matthew Wilcox wrote: > On Thu, Oct 29, 2020 at 09:02:31AM -0600, Jens Axboe wrote: >> On 10/29/20 8:57 AM, Matthew Wilcox wrote: >>> On Thu, Oct 29, 2020 at 07:57:34AM -0600, Jens Axboe wrote: >>>> On 10/28/20 4:26 PM, Jens Axboe wrote: >>>>> I did see some wins when I tested this. I'll try and run some testing >>>>> tomorrow and report back. If there's something specifically you want to >>>>> see tested, let me know. >>>> >>>> I did some testing, unfortunately it's _very_ hard to produce somewhat >>>> consistent and good numbers as it quickly becomes a game of kswapd. >>>> Here's a basic case of 4 threads doing 32k random reads: >>>> >>>> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND >>>> 462 root 20 0 0 0 0 R 65.5 0.0 0:08.02 kswapd0 >>>> 2287 axboe 20 0 1303448 2176 1072 R 46.6 0.0 0:05.35 fio >>>> 2289 axboe 20 0 1303456 2196 1092 D 46.6 0.0 0:05.34 fio >>>> 2290 axboe 20 0 1303460 2216 1112 D 46.6 0.0 0:05.37 fio >>>> 2288 axboe 20 0 1303452 2224 1120 R 45.9 0.0 0:05.33 fio >>>> >>>> Sad face... Unfortunately once kswapd kicks in, performance also >>>> plummets. This box only has 32G of ram, and you can fill that in less >>>> than 10 seconds doing buffered reads like that. >>>> >>>> I ran 4k and 32k testing, and using 1 and 4 threads. But given the above >>>> sadness, it quickly ends up looking the same for me. >>> >>> What if your workload actually fits in memory? That would seem to be >>> the situation where Kent's patches would make a difference. >> >> That was my point, if I do multi-page reads then memory is filled in >> seconds, which makes it pretty hard to provide any accurate numbers. I >> don't have anything slow in this test box, I'll see if I can find >> something to stick in it. > > I meant re-reading files which fit in memory, so you take ten seconds > to fill the page cache, then read from the same files over and over. That I can certainly try. -- Jens Axboe