Re: [PATCH] Btrfs: throttle delayed refs better

[Josef Bacik <jbacik@fb.com>]

On 01/24/2014 02:34 AM, Liu Bo wrote:
> On Thu, Jan 23, 2014 at 01:07:52PM -0500, Josef Bacik wrote:
>> On one of our gluster clusters we noticed some pretty big lag spikes.  This
>> turned out to be because our transaction commit was taking like 3 minutes to
>> complete.  This is because we have like 30 gigs of metadata, so our global
>> reserve would end up being the max which is like 512 mb.  So our throttling code
>> would allow a ridiculous amount of delayed refs to build up and then they'd all
>> get run at transaction commit time, and for a cold mounted file system that
>> could take up to 3 minutes to run.  So fix the throttling to be based on both
>> the size of the global reserve and how long it takes us to run delayed refs.
>> This patch tracks the time it takes to run delayed refs and then only allows 1
>> seconds worth of outstanding delayed refs at a time.  This way it will auto-tune
>> itself from cold cache up to when everything is in memory and it no longer has
>> to go to disk.  This makes our transaction commits take much less time to run.
>> Thanks,
> Which version of btrfs is the patch made for?
>
> I checked the code and it doesn't seem to be btrfs-next, either...we don't
> have a __btrfs_run_delayed_refs().

It depends on the patch I sent before where I move delayed refs onto a 
delayed ref head rb tree.  Thanks,

Josef