Re: çå: çå: [PATCH] mm/memcontrol.c: speed up to force empty a memory cgroup

[Andrey Ryabinin]

On 03/21/2018 01:15 AM, David Rientjes wrote:
> On Wed, 21 Mar 2018, Andrey Ryabinin wrote:
> 
>>>>> It would probably be best to limit the 
>>>>> nr_pages to the amount that needs to be reclaimed, though, rather than 
>>>>> over reclaiming.
>>>>
>>>> How do you achieve that? The charging path is not synchornized with the
>>>> shrinking one at all.
>>>>
>>>
>>> The point is to get a better guess at how many pages, up to 
>>> SWAP_CLUSTER_MAX, that need to be reclaimed instead of 1.
>>>
>>>>> If you wanted to be invasive, you could change page_counter_limit() to 
>>>>> return the count - limit, fix up the callers that look for -EBUSY, and 
>>>>> then use max(val, SWAP_CLUSTER_MAX) as your nr_pages.
>>>>
>>>> I am not sure I understand
>>>>
>>>
>>> Have page_counter_limit() return the number of pages over limit, i.e. 
>>> count - limit, since it compares the two anyway.  Fix up existing callers 
>>> and then clamp that value to SWAP_CLUSTER_MAX in 
>>> mem_cgroup_resize_limit().  It's a more accurate guess than either 1 or 
>>> 1024.
>>>
>>
>> JFYI, it's never 1, it's always SWAP_CLUSTER_MAX.
>> See try_to_free_mem_cgroup_pages():
>> ....	
>> 	struct scan_control sc = {
>> 		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
>>
> 
> Is SWAP_CLUSTER_MAX the best answer if I'm lowering the limit by 1GB?
> 

Absolutely not. I completely on your side here. 
I've tried to fix this recently - http://lkml.kernel.org/r/20180119132544.19569-2-aryabinin@xxxxxxxxxxxxx
I guess that Andrew decided to not take my patch, because Michal wasn't
happy about it (see mail archives if you want more details).