From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it1-f200.google.com (mail-it1-f200.google.com [209.85.166.200]) by kanga.kvack.org (Postfix) with ESMTP id 9D5748E00C0 for ; Tue, 11 Dec 2018 13:05:16 -0500 (EST) Received: by mail-it1-f200.google.com with SMTP id j202so8115039itj.1 for ; Tue, 11 Dec 2018 10:05:16 -0800 (PST) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id 130sor4390229ita.7.2018.12.11.10.05.15 for (Google Transport Security); Tue, 11 Dec 2018 10:05:15 -0800 (PST) Subject: Re: [PATCH] aio: Convert ioctx_table to XArray References: <20181128183531.5139-1-willy@infradead.org> <20181211175156.GF6830@bombadil.infradead.org> From: Jens Axboe Message-ID: <0f77a532-0d88-78bc-b9cc-06bb203a0405@kernel.dk> Date: Tue, 11 Dec 2018 11:05:12 -0700 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: 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 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... -- Jens Axboe