On Thu 26-01-12 11:25:56, Vivek Goyal wrote: > On Wed, Jan 25, 2012 at 02:35:52PM +0800, Wu Fengguang wrote: > > 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. > > Should it be a udev rule to change read_ahead_kb on device based on device > size, instead of a kernel patch? Yes, we talked about that and I think having the logic in udev rule is easier. Just if we decided the logic should use a lot of kernel internal state, then it's better to have it in kernel. > This is assuming device size is a good way to determine read ahead window > size. I would guess that device speed should also matter though isn't it. > If device is small but fast then it is probably ok to have larger read ahead > window and vice versa. Yes, but speed is harder to measure than size ;) Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
