Hi, On Tue, 2012-01-24 at 23:15 -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. 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. 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. > > Cheers, Andreas > If the reason for not setting a larger readahead value is just that it might increase memory pressure and thus decrease performance, is it possible to use a suitable metric from the VM in order to set the value automatically according to circumstances? Steve. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
