On Wednesday 17 of August 2016, Michal Hocko wrote:

On Wed 17-08-16 10:34:54, Arkadiusz Miśkiewicz wrote:
[...]

quoted

With "[PATCH] mm, oom: report compaction/migration stats for higher order
requests" patch:
https://ixion.pld-linux.org/~arekm/p2/ext4/log-20160817.txt

Didn't count much - all counters are 0
compaction_stall:0 compaction_fail:0 compact_migrate_scanned:0
compact_free_scanned:0 compact_isolated:0 pgmigrate_success:0
pgmigrate_fail:0

Dohh, COMPACTION counters are events and those are different than other
counters we have. They only have per-cpu representation and so we would
have to do
+       for_each_online_cpu(cpu) {
+               struct vm_event_state *this = &per_cpu(vm_event_states,
cpu); +               ret += this->event[item];
+       }

which is really nasty because, strictly speaking, we would have to do
{get,put}_online_cpus around that loop and that uses locking and we do
not want to possibly block in this path just because something is in the
middle of the hotplug. So let's scratch that patch for now and sorry I
haven't realized that earlier.

quoted

two processes were killed by OOM (rm and cp), the rest of rm/cp didn't
finish

and I'm interrupting it to try that next patch:

quoted

Could you try to test with
patch from
http://lkml.kernel.org/r/20160816031222.GC16913@js1304-P5Q-DELUXE
please? Ideally on top of linux-next. You can add both the compaction
counters patch in the oom report and high order atomic reserves patch
on top.

Uhm, was going to use it on top of 4.7.[01] first.

OK

So with  http://lkml.kernel.org/r/20160816031222.GC16913@js1304-P5Q-DELUXE
OOM no longer happens (all 10x rm/cp processes finished).

https://ixion.pld-linux.org/~arekm/p2/ext4/log-20160818.txt

On Wednesday 17 of August 2016, Jan Kara wrote:

Just one more debug idea to add on top of what Michal said: Can you enable
mm_shrink_slab_start and mm_shrink_slab_end tracepoints (via
/sys/kernel/debug/tracing/events/vmscan/mm_shrink_slab_{start,end}/enable)
and gather output from /sys/kernel/debug/tracing/trace_pipe while the copy
is running?

Here it is:

https://ixion.pld-linux.org/~arekm/p2/ext4/log-trace_pipe-20160818.txt.gz

-- 
Arkadiusz Miśkiewicz, arekm / ( maven.pl | pld-linux.org )

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