Re: lot of MemAvailable but falling cache and raising PSI - Stefan Priebe

From: Stefan Priebe - Profihost AG <s.priebe@profihost.ag>
To: Michal Hocko <mhocko@kernel.org>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
	l.roehrs@profihost.ag, cgroups@vger.kernel.org,
	Johannes Weiner <hannes@cmpxchg.org>,
	Vlastimil Babka <vbabka@suse.cz>
Subject: Re: lot of MemAvailable but falling cache and raising PSI
Date: Mon, 9 Sep 2019 14:56:39 +0200
Message-ID: <10fa0b97-631d-f82b-0881-89adb9ad5ded@profihost.ag> (raw)
In-Reply-To: <20190909124950.GN27159@dhcp22.suse.cz>

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.

I would try to find one with much higher pressure.

>  You've said that your machine
> doesn't have more than one NUMA node, right?

Yes the first example is / was a VM. This one is a Single Xeon.

Stefan