Re: [PATCH] Btrfs: throttle delayed refs better

[Johannes Hirte <johannes.hirte@datenkhaos.de>]

On Wed, 5 Feb 2014 16:46:57 -0500
Josef Bacik <jbacik@fb.com> wrote:

> 
> On 02/05/2014 04:42 PM, Johannes Hirte wrote:
> > On Wed, 5 Feb 2014 14:36:39 -0500
> > Josef Bacik <jbacik@fb.com> wrote:
> >
> >> On 02/05/2014 02:30 PM, Johannes Hirte wrote:
> >>> On Wed, 5 Feb 2014 14:00:57 -0500
> >>> Josef Bacik <jbacik@fb.com> wrote:
> >>>
> >>>> On 02/05/2014 12:34 PM, Johannes Hirte wrote:
> >>>>> On Wed, 5 Feb 2014 10:49:15 -0500
> >>>>> Josef Bacik <jbacik@fb.com> wrote:
> >>>>>
> >>>>>> Ok none of those make sense which makes me think it may be the
> >>>>>> ktime bits, instead of un-applying the whole patch could you
> >>>>>> just comment out the parts
> >>>>>>
> >>>>>>             ktime_t start = ktime_get();
> >>>>>>
> >>>>>> and
> >>>>>>
> >>>>>>             if (actual_count > 0) {
> >>>>>>                     u64 runtime =
> >>>>>> ktime_to_ns(ktime_sub(ktime_get(), start)); u64 avg;
> >>>>>>
> >>>>>>                     /*
> >>>>>>                      * We weigh the current average higher than
> >>>>>> our current runtime
> >>>>>>                      * to avoid large swings in the average.
> >>>>>>                      */
> >>>>>>                     spin_lock(&delayed_refs->lock);
> >>>>>>                     avg = fs_info->avg_delayed_ref_runtime * 3
> >>>>>> + runtime; avg = div64_u64(avg, 4);
> >>>>>>                     fs_info->avg_delayed_ref_runtime = avg;
> >>>>>>                     spin_unlock(&delayed_refs->lock);
> >>>>>>             }
> >>>>>>
> >>>>>> in __btrfs_run_delayed_refs and see if that makes the problem
> >>>>>> stop? If it does will you try chris's for-linus branch to see
> >>>>>> if it still reproduces there?  Maybe some patch changed
> >>>>>> ktime_get() in -rc1 that is causing issues and we're just now
> >>>>>> exposing it. Thanks,
> >>>>> With the ktime bits disabled, I wasn't able to reproduce the
> >>>>> problem anymore. With Chris' for-linus branch it took longer but
> >>>>> still appeared.
> >>>>>
> >>>> Ok can you send your .config, maybe there's some weird time bug
> >>>> being exposed.  What kind of CPU do you have?  Thanks,
> >>>>
> >>>> Josef
> >>> It's a Core i5-540M, dualcore + hyperthreading
> >> Ok while I'm doing this can you change
> >> btrfs_should_throttle_delayed_refs to _always_ return 1, still with
> >> all the ktime stuff commented out, and see if that causes the
> >> problem to happen?  Thanks,
> > Yes it does. Same behavior as without ktime stuff commented out.
> >
> Ok perfect, can you send me a btrfs fi df of that volume, and do you 
> have any snapshots or anything?  Thanks,

btrfs fi df /
Data, single: total=220.01GiB, used=210.85GiB
System, DUP: total=8.00MiB, used=32.00KiB
System, single: total=4.00MiB, used=0.00
Metadata, DUP: total=4.00GiB, used=2.93GiB
Metadata, single: total=8.00MiB, used=0.00

No snapshots but several subvolumes. / itself is a seperate subvolume
and subvol 0 only contains the other subvolumes (5 at moment). qgroups
aren't enabled.

mount options are noatime,inode_cache, if this matters

regards,
  Johannes