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Fri, 5 Jun 2020 19:02:45 -0400 (EDT) Date: Fri, 5 Jun 2020 16:02:44 -0700 From: Andres Freund To: Jens Axboe Cc: io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org Subject: Re: [PATCHSET v5 0/12] Add support for async buffered reads Message-ID: <20200605230244.u342xw4negic2nmr@alap3.anarazel.de> References: <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> <0e5b7a2d-eb0e-16e6-cc9f-c2ca5fe8cb92@kernel.dk> <20200605225429.s424lrrqhaseoa2h@alap3.anarazel.de> <0179d0bf-0b01-3f05-9221-654a00f0452d@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0179d0bf-0b01-3f05-9221-654a00f0452d@kernel.dk> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Hi, On 2020-06-05 16:56:44 -0600, Jens Axboe wrote: > On 6/5/20 4:54 PM, Andres Freund wrote: > > On 2020-06-05 16:49:24 -0600, Jens Axboe wrote: > >> 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. > > > > But I assume async would still work for files with POSIX_FADV_RANDOM > > set, or not? Assuming the system wide setting isn't zero, of course. > > Yes it'll work if FADV_RANDOM is set. Cool. > But just not if read-ahead is totally disabled. I guess we could make > that work too, though not sure that it's super important. It's not from my end. I was just trying to check if the reduced performance I saw was related to interactions between PG prefetching and kernel level prefetching. And changing the /sys entry seemed easier than making postgres set POSIX_FADV_RANDOM... Greetings, Andres Freund