Re: [dm-devel] [Lsf-pc] [LSF/MM TOPIC] a few storage topics

[Andreas Dilger <adilger dilger ca>]

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