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

[Michal Hocko <mhocko@suse.cz>]

On Thu 02-02-12 17:37:13, Ying Han 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>

For the global LRU removal
Acked-by: Michal Hocko <mhocko@suse.cz>

see the comment about the swap extension bellow.

Thanks

> ---
>  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
[...]
> @@ -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. 

Not really. It also helped inter-cgroup behavior. Consider an (anon) mem
hog which goes wild. You could end up with a full swap until it gets
killed which might be quite some time. With the swap extension, on the
other hand, you are able to stop it before it does too much damage.


-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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