From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH] aio: Convert ioctx_table to XArray From: Jens Axboe To: Jeff Moyer , Matthew Wilcox Cc: Alexander Viro , Benjamin LaHaise , Andrew Morton , Kees Cook , linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dan Carpenter , kent.overstreet@gmail.com References: <20181128183531.5139-1-willy@infradead.org> <20181211175156.GF6830@bombadil.infradead.org> <0f77a532-0d88-78bc-b9cc-06bb203a0405@kernel.dk> Message-ID: <6b9a45c4-47a2-4c44-aa7e-6e5e90eff9df@kernel.dk> Date: Tue, 11 Dec 2018 11:32:54 -0700 MIME-Version: 1.0 In-Reply-To: <0f77a532-0d88-78bc-b9cc-06bb203a0405@kernel.dk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: On 12/11/18 11:05 AM, Jens Axboe wrote: > On 12/11/18 11:02 AM, Jeff Moyer wrote: >> Matthew Wilcox writes: >> >>> On Tue, Dec 11, 2018 at 12:21:52PM -0500, Jeff Moyer wrote: >>>> I'm going to submit this version formally. If you're interested in >>>> converting the ioctx_table to xarray, you can do that separately from a >>>> security fix. I would include a performance analysis with that patch, >>>> though. The idea of using a radix tree for the ioctx table was >>>> discarded due to performance reasons--see commit db446a08c23d5 ("aio: >>>> convert the ioctx list to table lookup v3"). I suspect using the xarray >>>> will perform similarly. >>> >>> There's a big difference between Octavian's patch and mine. That patch >>> indexed into the radix tree by 'ctx_id' directly, which was pretty >>> much guaranteed to exhibit some close-to-worst-case behaviour from the >>> radix tree due to IDs being sparsely assigned. My patch uses the ring >>> ID which _we_ assigned, and so is nicely behaved, being usually a very >>> small integer. >> >> OK, good to know. I obviously didn't look too closely at the two. >> >>> What performance analysis would you find compelling? Octavian's original >>> fio script: >>> >>>> rw=randrw; size=256k ;directory=/mnt/fio; ioengine=libaio; iodepth=1 >>>> blocksize=1024; numjobs=512; thread; loops=100 >>>> >>>> on an EXT2 filesystem mounted on top of a ramdisk >>> >>> or something else? >> >> I think the most common use case is a small number of ioctx-s, so I'd >> like to see that use case not regress (that should be easy, right?). >> Kent, what were the tests you were using when doing this work? Jens, >> since you're doing performance work in this area now, are there any >> particular test cases you care about? > > I can give it a spin, ioctx lookup is in the fast path, and for "classic" > aio we do it twice for each IO... Don't see any regressions. But if we're fiddling with it anyway, can't we do something smarter? Make the fast path just index a table, and put all the big hammers in setup/destroy. We're spending a non-substantial amount of time doing lookups, that's really no different before and after the patch. -- Jens Axboe