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

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

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 ?

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

Thanks,
-Kame






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