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).
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