linux-kernel - Re: [PATCH] memcg: Fix documentation

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Date:	Wed, 8 Apr 2009 16:25:28 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	bharata@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] memcg: Fix documentation

Thank you, very helpful. but some nitpicks.


On Wed, 8 Apr 2009 12:48:17 +0530
Bharata B Rao <bharata@...ux.vnet.ibm.com> wrote:

> memcg: Fix documentation.
> 
> The description about various statistics from memory.stat is not accurate
> and confusing at times.
> 
> Correct this along with a few other minor cleanups.
> 
> Signed-off-by: Bharata B Rao <bharata@...ux.vnet.ibm.com>
> Cc: Balbir Singh <balbir@...ux.vnet.ibm.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
>  Documentation/cgroups/memory.txt |   50 +++++++++++++++++++++------------------
>  1 file changed, 28 insertions(+), 22 deletions(-)
> 
> --- a/Documentation/cgroups/memory.txt
> +++ b/Documentation/cgroups/memory.txt
> @@ -6,15 +6,14 @@ used here with the memory controller tha
>  
>  Salient features
>  
> -a. Enable control of both RSS (mapped) and Page Cache (unmapped) pages
> +a. Enable control of RSS (mapped), Page Cache (unmapped) and Swap cache
> +   (unmapped) pages.
      Enable control of Anonymous memory, Page Cache and Swap Cache. 
?

>  b. The infrastructure allows easy addition of other types of memory to control
>  c. Provides *zero overhead* for non memory controller users
>  d. Provides a double LRU: global memory pressure causes reclaim from the
>     global LRU; a cgroup on hitting a limit, reclaims from the per
>     cgroup LRU
>  
> -NOTE: Swap Cache (unmapped) is not accounted now.
> -
>  Benefits and Purpose of the memory controller
>  
>  The memory controller isolates the memory behaviour of a group of tasks
> @@ -290,34 +289,41 @@ will be charged as a new owner of it.
>    moved to the parent. If you want to avoid that, force_empty will be useful.
>  
>  5.2 stat file
> -  memory.stat file includes following statistics (now)
> -	cache			- # of pages from page-cache and shmem.
> -	rss			- # of pages from anonymous memory.
> -	pgpgin			- # of event of charging
> -	pgpgout			- # of event of uncharging
> -	active_anon		- # of pages on active lru of anon, shmem.
> -	inactive_anon 		- # of pages on active lru of anon, shmem
> -	active_file		- # of pages on active lru of file-cache
> -	inactive_file		- # of pages on inactive lru of file cache
> -	unevictable		- # of pages cannot be reclaimed.(mlocked etc)
> -
> -	Below is depend on CONFIG_DEBUG_VM.
> -	inactive_ratio		- VM inernal parameter. (see mm/page_alloc.c)
> -	recent_rotated_anon	- VM internal parameter. (see mm/vmscan.c)
> -	recent_rotated_file	- VM internal parameter. (see mm/vmscan.c)
> -	recent_scanned_anon 	- VM internal parameter. (see mm/vmscan.c)
> -	recent_scanned_file 	- VM internal parameter. (see mm/vmscan.c)
>  
> -  Memo:
> +memory.stat file includes following statistics
> +
> +cache		- # of bytes of page-cache memory.
> +rss		- # of bytes of anonymous memory.
                    This includes # of swap cache.

> +pgpgin		- # of pages paged in (equivalent to # of charging events).
> +pgpgout		- # of pages paged out (equivalent to # of uncharging events).
> +active_anon	- # of bytes of anonymous memory on active lru list.
                                anonymous memory + shared memory(tmpfs) + SwapCache.
                          Seeing acitive/inactive_file, how about swap-backed memory ?

> +inactive_anon	- # of bytes of anonymous memory on inactive lru list. 
> +active_file	- # of bytes of file-backed memory on active lru list.
> +inactive_file	- # of bytes of file-backed memory on inactive lru list.
> +unevictable	- # of bytes of memory that cannot be reclaimed (mlocked etc).
> +
> +The following additional stats are dependent on CONFIG_DEBUG_VM.
> +
> +inactive_ratio		- VM inernal parameter. (see mm/page_alloc.c)
> +recent_rotated_anon	- VM internal parameter. (see mm/vmscan.c)
> +recent_rotated_file	- VM internal parameter. (see mm/vmscan.c)
> +recent_scanned_anon	- VM internal parameter. (see mm/vmscan.c)
> +recent_scanned_file	- VM internal parameter. (see mm/vmscan.c)
> +
> +Memo:
>  	recent_rotated means recent frequency of lru rotation.
>  	recent_scanned means recent # of scans to lru.
>  	showing for better debug please see the code for meanings.
>  
> +Note:
> +	Only anonymous memory is listed as part of 'rss' stat. This should
> +	not be confused with the true 'resident set size' or the amount of
> +	physical memory used by the cgroup.
        To know the real value of resident-set-size, plz check each process's
        anon_rss and file_rss. per-cgroup rss accounting is not done now.

Thanks,
-Kame

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