From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wu Fengguang Subject: Re: [Lsf-pc] [dm-devel] [LSF/MM TOPIC] a few storage topics Date: Wed, 25 Jan 2012 14:35:52 +0800 Message-ID: <20120125063552.GA27375@localhost> References: <186EA560-1720-4975-AC2F-8C72C4A777A9@dilger.ca> <20120124184054.GA23227@infradead.org> <20120124190732.GH4387@shiny> <20120124200932.GB20650@quack.suse.cz> <20120124203936.GC20650@quack.suse.cz> <20120125032932.GA7150@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jan Kara , Jeff Moyer , Andrea Arcangeli , "linux-scsi@vger.kernel.org" , Mike Snitzer , "neilb@suse.de" , Christoph Hellwig , "dm-devel@redhat.com" , Boaz Harrosh , "linux-fsdevel@vger.kernel.org" , "lsf-pc@lists.linux-foundation.org" , Chris Mason , "Darrick J.Wong" To: Andreas Dilger Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Tue, Jan 24, 2012 at 11:15:13PM -0700, Andreas Dilger wrote: > On 2012-01-24, at 8:29 PM, Wu Fengguang wrote: > > On Tue, Jan 24, 2012 at 09:39:36PM +0100, Jan Kara wrote: > >> On Tue 24-01-12 15:13:40, Jeff Moyer wrote: > >>>> Maybe 128 KB is a too small default these days but OTOH noone prevents you > >>>> from raising it (e.g. SLES uses 1 MB as a default). > >>> > >>> For some reason, I thought it had been bumped to 512KB by default. Must > >>> be that overactive imagination I have... Anyway, if all of the distros > >>> start bumping the default, don't you think it's time to consider bumping > >>> it upstream, too? I thought there was a lot of work put into not being > >>> too aggressive on readahead, so the downside of having a larger > >>> read_ahead_kb setting was fairly small. > >> > >> Yeah, I believe 512KB should be pretty safe these days except for > >> embedded world. OTOH average desktop user doesn't really care so it's > >> mostly servers with beefy storage that care... (note that I wrote we raised > >> the read_ahead_kb for SLES but not for openSUSE or SLED (desktop enterprise > >> distro)). > > > > Maybe we don't need to care much about the embedded world when raising > > the default readahead size? Because even the current 128KB is too much > > for them, and I see Android setting the readahead size to 4KB... > > > > Some time ago I posted a series for raising the default readahead size > > to 512KB. But I'm open to use 1MB now (shall we vote on it?). > > I'm all in favour of 1MB (aligned) readahead. 1MB readahead aligned to i*1MB boundaries? I like this idea. It will work well if the filesystems employ the same alignment rule for large files. > I think the embedded folks > already set enough CONFIG opts that we could trigger on one of those > (e.g. CONFIG_EMBEDDED) to avoid stepping on their toes. Good point. We could add a configurable CONFIG_READAHEAD_KB=128 when CONFIG_EMBEDDED is selected. > It would also be > possible to trigger on the size of the device so that the 32MB USB stick > doesn't sit busy for a minute with readahead that is useless. Yeah, I do have a patch for shrinking readahead size based on device size. Thanks, Fengguang