Re: [RFC][PATCH] another swap controller for cgroup

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

YAMAMOTO Takashi wrote:
>> YAMAMOTO Takashi wrote:
>>> hi,
>>>
>>>> Daisuke Nishimura wrote:
>>>>> Hi, Yamamoto-san.
>>>>>
>>>>> I'm reviewing and testing your patch now.
>>>>>
>>>> In building kernel infinitely(in a cgroup of
>>>> memory.limit=64M and swap.limit=128M, with swappiness=100),
>>>> almost all of the swap (1GB) is consumed as swap cache
>>>> after a day or so.
>>>> As a result, processes are occasionally OOM-killed even when
>>>> the swap.usage of the group doesn't exceed the limit.
>>>>
>>>> I don't know why the swap cache uses up swap space.
>>>> I will test whether a similar issue happens without your patch.
>>>> Do you have any thoughts?
>>> my patch tends to yield more swap cache because it makes try_to_unmap
>>> fail and shrink_page_list leaves swap cache in that case.
>>> i'm not sure how it causes 1GB swap cache, tho.
>>>
>> Agree.
>>
>> I suspected that the cause of this problem was the behavior
>> of shrink_page_list as you said, so I thought one of Rik's
>> split-lru patchset:
>>
>>   http://lkml.org/lkml/2008/3/4/492
>>   [patch 04/20] free swap space on swap-in/activation
>>
>> would reduce the usage of swap cache to half of the total swap.
>> But it didn't help, so I think there may be some other causes.
> 
> do you mean you tested with the patch in the url?
> i don't think remove_exclusive_swap_page works for us
> because our page has more references than it expects.
> ie. ptes, cache, isolate_page
> 
umm... you are right.

I missed the fact that isolate_page increases page count.


Thanks,
Daisuke Nishimura.


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