Re: [PATCH 2/2] mm/vmscan: calculate reclaimed slab caches in all reclaim paths

[Kirill Tkhai <ktkhai@virtuozzo.com>]

On 24.06.2019 15:30, Yafang Shao wrote:
> On Mon, Jun 24, 2019 at 4:53 PM Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
>>
>> On 21.06.2019 13:14, Yafang Shao wrote:
>>> There're six different reclaim paths by now,
>>> - kswapd reclaim path
>>> - node reclaim path
>>> - hibernate preallocate memory reclaim path
>>> - direct reclaim path
>>> - memcg reclaim path
>>> - memcg softlimit reclaim path
>>>
>>> The slab caches reclaimed in these paths are only calculated in the above
>>> three paths.
>>>
>>> There're some drawbacks if we don't calculate the reclaimed slab caches.
>>> - The sc->nr_reclaimed isn't correct if there're some slab caches
>>>   relcaimed in this path.
>>> - The slab caches may be reclaimed thoroughly if there're lots of
>>>   reclaimable slab caches and few page caches.
>>>   Let's take an easy example for this case.
>>>   If one memcg is full of slab caches and the limit of it is 512M, in
>>>   other words there're approximately 512M slab caches in this memcg.
>>>   Then the limit of the memcg is reached and the memcg reclaim begins,
>>>   and then in this memcg reclaim path it will continuesly reclaim the
>>>   slab caches until the sc->priority drops to 0.
>>>   After this reclaim stops, you will find there're few slab caches left,
>>>   which is less than 20M in my test case.
>>>   While after this patch applied the number is greater than 300M and
>>>   the sc->priority only drops to 3.
>>>
>>> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
>>> ---
>>>  mm/vmscan.c | 7 +++++++
>>>  1 file changed, 7 insertions(+)
>>>
>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>> index 18a66e5..d6c3fc8 100644
>>> --- a/mm/vmscan.c
>>> +++ b/mm/vmscan.c
>>> @@ -3164,11 +3164,13 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
>>>       if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
>>>               return 1;
>>>
>>> +     current->reclaim_state = &sc.reclaim_state;
>>>       trace_mm_vmscan_direct_reclaim_begin(order, sc.gfp_mask);
>>>
>>>       nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
>>>
>>>       trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
>>> +     current->reclaim_state = NULL;
>>
>> Shouldn't we remove reclaim_state assignment from __perform_reclaim() after this?
>>
> 
> Oh yes. We should remove it. Thanks for pointing out.
> I will post a fix soon.

With the change above, feel free to add my Reviewed-by: to all of the series.

Kirill