Am 10.09.19 um 10:29 schrieb Michal Hocko:
> On Tue 10-09-19 07:56:36, Stefan Priebe - Profihost AG wrote:
>>
>> Am 09.09.19 um 14:56 schrieb Stefan Priebe - Profihost AG:
>>> Am 09.09.19 um 14:49 schrieb Michal Hocko:
>>>> On Mon 09-09-19 14:37:52, Stefan Priebe - Profihost AG wrote:
>>>>>
>>>>> Am 09.09.19 um 14:28 schrieb Michal Hocko:
>>>>>> On Mon 09-09-19 14:10:02, Stefan Priebe - Profihost AG wrote:
>>>>>>>
>>>>>>> Am 09.09.19 um 14:08 schrieb Michal Hocko:
>>>>>>>> On Mon 09-09-19 13:01:36, Michal Hocko wrote:
>>>>>>>>> and that matches moments when we reclaimed memory. There seems to be a
>>>>>>>>> steady THP allocations flow so maybe this is a source of the direct
>>>>>>>>> reclaim?
>>>>>>>>
>>>>>>>> I was thinking about this some more and THP being a source of reclaim
>>>>>>>> sounds quite unlikely. At least in a default configuration because we
>>>>>>>> shouldn't do anything expensinve in the #PF path. But there might be a
>>>>>>>> difference source of high order (!costly) allocations. Could you check
>>>>>>>> how many allocation requests like that you have on your system?
>>>>>>>>
>>>>>>>> mount -t debugfs none /debug
>>>>>>>> echo "order > 0" > /debug/tracing/events/kmem/mm_page_alloc/filter
>>>>>>>> echo 1 > /debug/tracing/events/kmem/mm_page_alloc/enable
>>>>>>>> cat /debug/tracing/trace_pipe > $file
>>>>>>
>>>>>> echo 1 > /debug/tracing/events/vmscan/mm_vmscan_direct_reclaim_begin/enable
>>>>>> echo 1 > /debug/tracing/events/vmscan/mm_vmscan_direct_reclaim_end/enable
>>>>>>
>>>>>> might tell us something as well but it might turn out that it just still
>>>>>> doesn't give us the full picture and we might need
>>>>>> echo stacktrace > /debug/tracing/trace_options
>>>>>>
>>>>>> It will generate much more output though.
>>>>>>
>>>>>>> Just now or when PSI raises?
>>>>>>
>>>>>> When the excessive reclaim is happening ideally.
>>>>>
>>>>> This one is from a server with 28G memfree but memory pressure is still
>>>>> jumping between 0 and 10%.
>>>>>
>>>>> I did:
>>>>> echo "order > 0" >
>>>>> /sys/kernel/debug/tracing/events/kmem/mm_page_alloc/filter
>>>>>
>>>>> echo 1 > /sys/kernel/debug/tracing/events/kmem/mm_page_alloc/enable
>>>>>
>>>>> echo 1 >
>>>>> /sys/kernel/debug/tracing/events/vmscan/mm_vmscan_direct_reclaim_begin/enable
>>>>>
>>>>> echo 1 >
>>>>> /sys/kernel/debug/tracing/events/vmscan/mm_vmscan_direct_reclaim_end/enable
>>>>>
>>>>> timeout 120 cat /sys/kernel/debug/tracing/trace_pipe > /trace
>>>>>
>>>>> File attached.
>>>>
>>>> There is no reclaim captured in this trace dump.
>>>> $ zcat trace1.gz | sed 's@.*\(order=[0-9]\).*\(gfp_flags=.*\)@\1 \2@' | sort | uniq -c
>>>> 777 order=1 gfp_flags=__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC
>>>> 663 order=1 gfp_flags=__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC
>>>> 153 order=1 gfp_flags=__GFP_IO|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC
>>>> 911 order=1 gfp_flags=GFP_KERNEL_ACCOUNT|__GFP_ZERO
>>>> 4872 order=1 gfp_flags=GFP_NOWAIT|__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_COMP|__GFP_ACCOUNT
>>>> 62 order=1 gfp_flags=GFP_NOWAIT|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC
>>>> 14 order=2 gfp_flags=GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP
>>>> 11 order=2 gfp_flags=GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_RECLAIMABLE
>>>> 1263 order=2 gfp_flags=__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC
>>>> 45 order=2 gfp_flags=__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_RECLAIMABLE
>>>> 1 order=2 gfp_flags=GFP_KERNEL|__GFP_COMP|__GFP_ZERO
>>>> 7853 order=2 gfp_flags=GFP_NOWAIT|__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_COMP|__GFP_ACCOUNT
>>>> 73 order=3 gfp_flags=__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC
>>>> 729 order=3 gfp_flags=__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_RECLAIMABLE
>>>> 528 order=3 gfp_flags=__GFP_IO|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC
>>>> 1203 order=3 gfp_flags=GFP_NOWAIT|__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_COMP|__GFP_ACCOUNT
>>>> 5295 order=3 gfp_flags=GFP_NOWAIT|__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP
>>>> 1 order=3 gfp_flags=GFP_NOWAIT|__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC
>>>> 132 order=3 gfp_flags=GFP_NOWAIT|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC
>>>> 13 order=5 gfp_flags=GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_ZERO
>>>> 1 order=6 gfp_flags=GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_ZERO
>>>> 1232 order=9 gfp_flags=GFP_TRANSHUGE
>>>> 108 order=9 gfp_flags=GFP_TRANSHUGE|__GFP_THISNODE
>>>> 362 order=9 gfp_flags=GFP_TRANSHUGE_LIGHT|__GFP_THISNODE
>>>>
>>>> Nothing really stands out because except for the THP ones none of others
>>>> are going to even be using movable zone.
>>> It might be that this is not an ideal example is was just the fastest i
>>> could find. May be we really need one with much higher pressure.
>>
>> here another trace log where a system has 30GB free memory but is under
>> constant pressure and does not build up any file cache caused by memory
>> pressure.
>
> So the reclaim is clearly induced by THP allocations
> $ zgrep vmscan trace2.gz | grep gfp_flags | sed 's@.*\(gfp_flags=.*\) .*@\1@' | sort | uniq -c
> 1580 gfp_flags=GFP_TRANSHUGE
> 15 gfp_flags=GFP_TRANSHUGE|__GFP_THISNODE
>
> $ zgrep vmscan trace2.gz | grep nr_reclaimed | sed 's@nr_reclaimed=@@' | awk '{nr+=$6+0}END{print nr}'
> 1541726
>
> 6GB of memory reclaimed in 1776s. That is a lot! But the THP allocation
> rate is really high as well
> $ zgrep "page_alloc.*GFP_TRANSHUGE" trace2.gz | wc -l
> 15340
>
> this is 30GB worth of THPs (some of them might get released of course).
> Also only 10% of requests ends up reclaiming.
>
> One additional interesting point
> $ zgrep vmscan trace2.gz | grep nr_reclaimed | sed 's@.*nr_reclaimed=\([[0-9]*\)@\1@' | calc_min_max.awk
> min: 1.00 max: 2792.00 avg: 965.99 std: 331.12 nr: 1596
>
> Even though the std is high there are quite some outliers when a lot of
> memory is reclaimed.
>
> Which kernel version is this. And again, what is the THP configuration.
This is 4.19.66 regarding THP you mean this:
/sys/kernel/mm/transparent_hugepage/defrag:always defer [defer+madvise]
madvise never
/sys/kernel/mm/transparent_hugepage/enabled:[always] madvise never
/sys/kernel/mm/transparent_hugepage/hpage_pmd_size:2097152
/sys/kernel/mm/transparent_hugepage/shmem_enabled:always within_size
advise [never] deny force
/sys/kernel/mm/transparent_hugepage/use_zero_page:1
/sys/kernel/mm/transparent_hugepage/enabled was madvise until yesterday
where i tried to switch to defer+madvise - which didn't help.
Greets,
Stefan
