Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1456628

Re: [dm-devel] [RFC PATCH 2/2] mm, mempool: do not throttle PF_LESS_THROTTLE tasks

Show all headers | View raw

On Wed, 3 Aug 2016, Michal Hocko wrote:

> > > Even mempool allocations shouldn't allow reclaim to
> > > scan pages too quickly even when LRU lists are full of dirty pages. But
> > > as I've said that would restrict the success rates even under light page
> > > cache load. Throttling on the wait_iff_congested should be quite rare.
> > > 
> > > Anyway do you see an excessive throttling with the patch posted
> > > http://lkml.kernel.org/r/20160725192344.GD2166@dhcp22.suse.cz ? Or from
> > 
> > It didn't have much effect.
> > 
> > Since the patch 4e390b2b2f34b8daaabf2df1df0cf8f798b87ddb (revert of the 
> > limitless mempool allocations), swapping to dm-crypt works in the simple 
> > example.
> 
> OK. Do you see any throttling due to wait_iff_congested?

No, but I've seen occasional stalls of mempool allocations in 
throttle_vm_writeout - but the patch that removed throttle_vm_writeout 
didn't improve overall speed, so the stalls were only minor.

> writeback_wait_iff_congested trace point should help here. If not maybe
> we should start with the above patch and see how it works in practise.
> If the there is still an excessive and unexpected throttling then we
> should move on to a more mempool/block layer users specific solution.

Currently, dm-crypt reports the device congested only if the underlying 
block device is congested.

But as others suggested, dm-crypt should report congested status if is 
clogged due to slow encryption progress - and in that case you should not 
throttle mempool allocations (because such throttling would decrease 
encryption speed even more).

Mikulas

> -- 
> Michal Hocko
> SUSE Labs

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: [RFC PATCH 2/2] mm, mempool: do not throttle PF_LESS_THROTTLE  tasks Mikulas Patocka <mpatocka@redhat.com> - 2016-07-26 00:00 +0200
  Re: [RFC PATCH 2/2] mm, mempool: do not throttle PF_LESS_THROTTLE  tasks Michal Hocko <mhocko@kernel.org> - 2016-07-26 09:30 +0200
  Re: [dm-devel] [RFC PATCH 2/2] mm, mempool: do not throttle PF_LESS_THROTTLE tasks NeilBrown <neilb@suse.com> - 2016-07-27 06:10 +0200
    Re: [dm-devel] [RFC PATCH 2/2] mm, mempool: do not throttle  PF_LESS_THROTTLE tasks Mikulas Patocka <mpatocka@redhat.com> - 2016-07-27 16:30 +0200
      Re: [dm-devel] [RFC PATCH 2/2] mm, mempool: do not throttle  PF_LESS_THROTTLE tasks Michal Hocko <mhocko@kernel.org> - 2016-07-27 20:50 +0200
        Re: [dm-devel] [RFC PATCH 2/2] mm, mempool: do not throttle  PF_LESS_THROTTLE tasks Mikulas Patocka <mpatocka@redhat.com> - 2016-08-03 16:30 +0200
          Re: [dm-devel] [RFC PATCH 2/2] mm, mempool: do not throttle  PF_LESS_THROTTLE tasks Michal Hocko <mhocko@kernel.org> - 2016-08-03 16:50 +0200
            Re: [dm-devel] [RFC PATCH 2/2] mm, mempool: do not throttle  PF_LESS_THROTTLE tasks Mikulas Patocka <mpatocka@redhat.com> - 2016-08-04 20:50 +0200
      Re: [dm-devel] [RFC PATCH 2/2] mm, mempool: do not throttle PF_LESS_THROTTLE tasks NeilBrown <neilb@suse.com> - 2016-07-27 23:40 +0200

csiph-web