Re: rsync: page allocation stalls in kernel 4.9.10 to a VessRAID NAS

[Robert Kudyba]

> On Feb 28, 2017, at 11:56 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> 
> On Tue 28-02-17 11:19:33, Robert Kudyba wrote:
>> 
>>> On Feb 28, 2017, at 10:15 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
>>> 
>>> On Tue 28-02-17 09:59:35, Robert Kudyba wrote:
>>>> 
>>>>> On Feb 28, 2017, at 9:40 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
>>>>> 
>>>>> On Tue 28-02-17 09:33:49, Robert Kudyba wrote:
>>>>>> 
>>>>>>> On Feb 28, 2017, at 9:15 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
>>>>>>> and this one is hitting the min watermark while there is not really
>>>>>>> much to reclaim. Only the page cache which might be pinned and not
>>>>>>> reclaimable from this context because this is GFP_NOFS request. It is
>>>>>>> not all that surprising the reclaim context fights to get some memory.
>>>>>>> There is a huge amount of the reclaimable slab which probably just makes
>>>>>>> a slow progress.
>>>>>>> 
>>>>>>> That is not something completely surprsing on 32b system I am afraid.
>>>>>>> 
>>>>>>> Btw. is the stall repeating with the increased time or it gets resolved
>>>>>>> eventually?
>>>>>> 
>>>>>> Yes and if you mean by repeating itâs not only affecting rsync but
>>>>>> you can see just now automount and NetworkManager get these page
>>>>>> allocation stalls and kswapd0 is getting heavy CPU load, are there any
>>>>>> other settings I can adjust?
>>>>> 
>>>>> None that I am aware of. You might want to talk to FS guys, maybe they
>>>>> can figure out who is pinning file pages so that they cannot be
>>>>> reclaimed. They do not seem to be dirty or under writeback. It would be
>>>>> also interesting to see whether that is a regression. The warning is
>>>>> relatively new so you might have had this problem before just haven't
>>>>> noticed it.
>>>> 
>>>> We have been getting out of memory errors for a while but those seem
>>>> to have gone away.
>>> 
>>> this sounds suspicious. Are you really sure that this is a new problem?
>>> Btw. is there any reason to use 32b kernel at all? It will always suffer
>>> from a really small lowmemâ
>> 
>> No this has been a problem for a while. Not sure if this server can
>> handle 64b itâs a bit old.
> 
> Ok, this is unfortunate. There is usually not much interest to fixing
> 32b issues which are inherent to the used memory model and which are not
> regressions which would be fixable, I am afraid.
> 
>>>> We did just replace the controller in the VessRAID
>>>> as there were some timeouts observed and multiple login/logout
>>>> attempts.
>>>> 
>>>> By FS guys do you mean the linux-fsdevel or linux-fsf list?
>>> 
>>> yeah linux-fsdevel. No idea what linux-fsf is. It would be great if you
>>> could collect some tracepoints before reporting the issue. At least
>>> those in events/vmscan/*.
>> 
>> Will do hereâs a perf report:
> 
> this will not tell us much. Tracepoints have much better chance to tell
> us how reclaim is progressing.

I have SystemTap configured are there any scripts in the SystemTap_Beginners_Guide.pdf that I can run to help? Sorry Iâm brand new to tracepoints. 

I do see these âvmscanâ from this command:
stap -L 'kernel.trace("*")'|sort

kernel.trace("vmscan:mm_shrink_slab_end") $shr:struct shrinker* $nid:int $shrinker_retval:int $unused_scan_cnt:long int $new_scan_cnt:long int $total_scan:long int
kernel.trace("vmscan:mm_shrink_slab_start") $shr:struct shrinker* $sc:struct shrink_control* $nr_objects_to_shrink:long int $pgs_scanned:long unsigned int $lru_pgs:long unsigned int $cache_items:long unsigned int $delta:long long unsigned int $total_scan:long unsigned int
kernel.trace("vmscan:mm_vmscan_direct_reclaim_begin") $order:int $may_writepage:int $gfp_flags:gfp_t $classzone_idx:int
kernel.trace("vmscan:mm_vmscan_direct_reclaim_end") $nr_reclaimed:long unsigned int
kernel.trace("vmscan:mm_vmscan_kswapd_sleep") $nid:int
kernel.trace("vmscan:mm_vmscan_kswapd_wake") $nid:int $zid:int $order:int
kernel.trace("vmscan:mm_vmscan_lru_isolate") $classzone_idx:int $order:int $nr_requested:long unsigned int $nr_scanned:long unsigned int $nr_taken:long unsigned int $isolate_mode:isolate_mode_t $file:int
kernel.trace("vmscan:mm_vmscan_lru_shrink_inactive") $nid:int $nr_scanned:long unsigned int $nr_reclaimed:long unsigned int $priority:int $file:int
kernel.trace("vmscan:mm_vmscan_memcg_isolate") $classzone_idx:int $order:int $nr_requested:long unsigned int $nr_scanned:long unsigned int $nr_taken:long unsigned int $isolate_mode:isolate_mode_t $file:int
kernel.trace("vmscan:mm_vmscan_memcg_reclaim_begin") $order:int $may_writepage:int $gfp_flags:gfp_t $classzone_idx:int
kernel.trace("vmscan:mm_vmscan_memcg_reclaim_end") $nr_reclaimed:long unsigned int
kernel.trace("vmscan:mm_vmscan_memcg_softlimit_reclaim_begin") $order:int $may_writepage:int $gfp_flags:gfp_t $classzone_idx:int
kernel.trace("vmscan:mm_vmscan_memcg_softlimit_reclaim_end") $nr_reclaimed:long unsigned int
kernel.trace("vmscan:mm_vmscan_wakeup_kswapd") $nid:int $zid:int $order:int
kernel.trace("vmscan:mm_vmscan_writepage") $page:struct page*