Re: page allocation stall in kernel 4.9 when copying files from one btrfs hdd to another

[Xin Zhou]

Hi,

The dirty data is in large amount, probably unable to commit to disk.
And this seems to happen when copying from 7200rpm to 5600rpm disks, according to previous post.

Probably the I/Os are buffered and pending, unable to get finished in-time.
It might be helpful to know if this only happens for specific types of 5600 rpm disks?

And are these disks on RAID groups? Thanks.
Xin
Â
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Sent:ÂWednesday, December 14, 2016 at 3:38 AM
From:Âadmin <admin@xxxxxxxxx>
To:Â"Michal Hocko" <mhocko@xxxxxxxxxx>
Cc:Âlinux-btrfs@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, "David Sterba" <dsterba@xxxxxxx>, "Chris Mason" <clm@xxxxxx>
Subject:ÂRe: page allocation stall in kernel 4.9 when copying files from one btrfs hdd to another
Hi,

I verified the log files and see no prior oom killer invocation. Unfortunately the machine has been rebooted since. Next time it happens, I will also look in dmesg.

Thanks,
David Arendt


Michal Hocko â Wed., 14. December 2016 11:31
> Btw. the stall should be preceded by the OOM killer invocation. Could
> you share the OOM report please. I am asking because such an OOM killer
> would be clearly pre-mature as per your meminfo. I am trying to change
> that code and seeing your numbers might help me.
>
> Thanks!
>
> On Wed 14-12-16 11:17:43, Michal Hocko wrote:
> > On Tue 13-12-16 18:11:01, David Arendt wrote:
> > > Hi,
> > >
> > > I receive the following page allocation stall while copying lots of
> > > large files from one btrfs hdd to another.
> > >
> > > Dec 13 13:04:29 server kernel: kworker/u16:8: page allocation stalls for 12260ms, order:0, mode:0x2400840(GFP_NOFS|__GFP_NOFAIL)
> > > Dec 13 13:04:29 server kernel: CPU: 0 PID: 24959 Comm: kworker/u16:8 Tainted: P O 4.9.0 #1
> > [...]
> > > Dec 13 13:04:29 server kernel: Call Trace:
> > > Dec 13 13:04:29 server kernel: [<ffffffff813f3a59>] ? dump_stack+0x46/0x5d
> > > Dec 13 13:04:29 server kernel: [<ffffffff81114fc1>] ? warn_alloc+0x111/0x130
> > > Dec 13 13:04:33 server kernel: [<ffffffff81115c38>] ? __alloc_pages_nodemask+0xbe8/0xd30
> > > Dec 13 13:04:33 server kernel: [<ffffffff8110de74>] ? pagecache_get_page+0xe4/0x230
> > > Dec 13 13:04:33 server kernel: [<ffffffff81323a8b>] ? alloc_extent_buffer+0x10b/0x400
> > > Dec 13 13:04:33 server kernel: [<ffffffff812ef8c5>] ? btrfs_alloc_tree_block+0x125/0x560
> >
> > OK, so this is
> > find_or_create_page(mapping, index, GFP_NOFS|__GFP_NOFAIL)
> >
> > The main question is whether this really needs to be NOFS request...
> >
> > > Dec 13 13:04:33 server kernel: [<ffffffff8132442f>] ? read_extent_buffer_pages+0x21f/0x280
> > > Dec 13 13:04:33 server kernel: [<ffffffff812d81f1>] ? __btrfs_cow_block+0x141/0x580
> > > Dec 13 13:04:33 server kernel: [<ffffffff812d87b0>] ? btrfs_cow_block+0x100/0x150
> > > Dec 13 13:04:33 server kernel: [<ffffffff812dc1d9>] ? btrfs_search_slot+0x1e9/0x9c0
> > > Dec 13 13:04:33 server kernel: [<ffffffff8131ead2>] ? __set_extent_bit+0x512/0x550
> > > Dec 13 13:04:33 server kernel: [<ffffffff812e1ab5>] ? lookup_inline_extent_backref+0xf5/0x5e0
> > > Dec 13 13:04:34 server kernel: [<ffffffff8131f0a4>] ? set_extent_bit+0x24/0x30
> > > Dec 13 13:04:34 server kernel: [<ffffffff812e4334>] ? update_block_group.isra.34+0x114/0x380
> > > Dec 13 13:04:34 server kernel: [<ffffffff812e4694>] ? __btrfs_free_extent.isra.35+0xf4/0xd20
> > > Dec 13 13:04:34 server kernel: [<ffffffff8134d561>] ? btrfs_merge_delayed_refs+0x61/0x5d0
> > > Dec 13 13:04:34 server kernel: [<ffffffff812e8bd2>] ? __btrfs_run_delayed_refs+0x902/0x10a0
> > > Dec 13 13:04:34 server kernel: [<ffffffff812ec0f0>] ? btrfs_run_delayed_refs+0x90/0x2a0
> > > Dec 13 13:04:34 server kernel: [<ffffffff812ec384>] ? delayed_ref_async_start+0x84/0xa0
> >
> > What would cause the reclaim recursion?
> >
> > > Dec 13 13:04:34 server kernel: Mem-Info:
> > > Dec 13 13:04:34 server kernel: active_anon:20 inactive_anon:34
> > > isolated_anon:0\x0a active_file:7370032 inactive_file:450105
> > > isolated_file:320\x0a unevictable:0 dirty:522748 writeback:189
> > > unstable:0\x0a slab_reclaimable:178255 slab_unreclaimable:124617\x0a
> > > mapped:4236 shmem:0 pagetables:1163 bounce:0\x0a free:38224 free_pcp:241
> > > free_cma:0
> >
> > This speaks for itself. There is a lot of dirty data, basically no
> > anonymous memory and GFP_NOFS cannot do much to reclaim obviously. This
> > is either a configuraion bug as somebody noted down the thread (setting
> > the dirty_ratio) or suboptimality of the btrfs code which might request
> > NOFS even though it is not strictly necessary. This would be more for
> > btrfs developers.
> > --
> > Michal Hocko
> > SUSE Labs
>
> --
> Michal Hocko
> SUSE Labs
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