Re: [PATCH] memcg: fix up documentation on global LRU.

[Ying Han <yinghan@google.com>]

On Thu, Feb 2, 2012 at 6:38 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Thu,  2 Feb 2012 17:37:13 -0800
> Ying Han <yinghan@google.com> wrote:
>
>> In v3.3-rc1, the global LRU has been removed with commit
>> "mm: make per-memcg LRU lists exclusive". The patch fixes up the memcg docs.
>>
>> Signed-off-by: Ying Han <yinghan@google.com>
>> ---
>>  Documentation/cgroups/memory.txt |   25 ++++++++++++-------------
>>  1 files changed, 12 insertions(+), 13 deletions(-)
>>
>> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
>> index 4c95c00..847a2a4 100644
>> --- a/Documentation/cgroups/memory.txt
>> +++ b/Documentation/cgroups/memory.txt
>> @@ -34,8 +34,7 @@ Current Status: linux-2.6.34-mmotm(development version of 2010/April)
>>
>>  Features:
>>   - accounting anonymous pages, file caches, swap caches usage and limiting them.
>> - - private LRU and reclaim routine. (system's global LRU and private LRU
>> -   work independently from each other)
>> + - pages are linked to per-memcg LRU exclusively, and there is no global LRU.
>>   - optionally, memory+swap usage can be accounted and limited.
>>   - hierarchical accounting
>>   - soft limit
>> @@ -154,7 +153,7 @@ updated. page_cgroup has its own LRU on cgroup.
>>  2.2.1 Accounting details
>>
>>  All mapped anon pages (RSS) and cache pages (Page Cache) are accounted.
>> -Some pages which are never reclaimable and will not be on the global LRU
>> +Some pages which are never reclaimable and will not be on the LRU
>>  are not accounted. We just account pages under usual VM management.
>>
>>  RSS pages are accounted at page_fault unless they've already been accounted
>> @@ -209,19 +208,19 @@ In this case, setting memsw.limit_in_bytes=3G will prevent bad use of swap.
>>  By using memsw limit, you can avoid system OOM which can be caused by swap
>>  shortage.
>>
>> -* why 'memory+swap' rather than swap.
>> -The global LRU(kswapd) can swap out arbitrary pages. Swap-out means
>> -to move account from memory to swap...there is no change in usage of
>> -memory+swap. In other words, when we want to limit the usage of swap without
>> -affecting global LRU, memory+swap limit is better than just limiting swap from
>> -OS point of view.
>> -
>>  * What happens when a cgroup hits memory.memsw.limit_in_bytes
>>  When a cgroup hits memory.memsw.limit_in_bytes, it's useless to do swap-out
>>  in this cgroup. Then, swap-out will not be done by cgroup routine and file
>> -caches are dropped. But as mentioned above, global LRU can do swapout memory
>> -from it for sanity of the system's memory management state. You can't forbid
>> -it by cgroup.
>> +caches are dropped.
>> +
>> +TODO:
>> +* use 'memory+swap' rather than swap was due to existence of global LRU. It can
>> +swap out arbitrary pages. Swap-out means to move account from memory to swap...
>> +there is no change in usage of memory+swap. In other words, when we want to
>> +limit the usage of swap without affecting global LRU, memory+swap limit is
>> +better than just limiting swap from OS point of view. However, the global LRU
>> +has been removed now and all pages are linked in private LRU. We might want to
>> +revisit this in the future.
>>
>
> Could you devide this memory+swap discussion to otehr patch ?

yes, will do that.

>
> Do you want to do memory locking by setting swap_limit=0 ?

hmm, not sure what do you mean here?

--Ying
>
> Thanks,
> -Kame
>
>
>
>
>
>

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