Re: memo: mem+swap controller

[Balbir Singh <balbir@linux.vnet.ibm.com>]

KAMEZAWA Hiroyuki wrote:
> Hi, mem+swap controller is suggested by Hugh Dickins and I think it's a great
> idea. Its concept is having 2 limits. (please point out if I misunderstand.)
> 
>  - memory.limit_in_bytes       .... limit memory usage.
>  - memory.total_limit_in_bytes .... limit memory+swap usage.
> 
> By this, we can avoid excessive use of swap under a cgroup without any bad effect
> to global LRU. (in page selection algorithm...overhead will be added, of course)
> 
> Following is state transition and counter handling design memo.
> This uses "3" counters to handle above conrrectly. If you have other logic,
> please teach me. (and blame me if my diagram is broken.)
> 
> A point is how to handle swap-cache, I think.
> (Maybe we need a _big_ change in memcg.)
> 

Could you please describe the big change? What do you have in mind?

> ==
> 
> state definition
>   new alloc  .... an object is newly allocated
>   no_swap    .... an object with page without swp_entry
>   swap_cache .... an object with page with swp_entry
>   disk_swap  .... an object without page with swp_entry
>   freed      .... an object is freed (by munmap)
> 
> (*) an object is an enitity which is accoutned, page or swap.
> 
>  new alloc ->  no_swap  <=>  swap_cache  <=>  disk_swap
>                  |             |                 |
>   freed.   <-----------<-------------<-----------
> 
> use 3 counters, no_swap, swap_cache, disk_swap.
> 
>     on_memory = no_swap + swap_cache.
>     total     = no_swap + swap_cache + disk_swap
> 
> on_memory is limited by memory.limit_in_bytes
> total     is limtied by memory.total_limit_in_bytes.
> 
>                      no_swap  swap_cache  disk_swap  on_memory  total
> new alloc->no_swap     +1         -           -         +1        +1
> no_swap->swap_cache    -1        +1           -         -         -
> swap_cache->no_swap    +1        -1           -         -         -
> swap_cache->disk_swap  -         -1           +1        -1        -
> disk_swap->swap_cache  -         +1           -1        +1        -
> no_swap->freed         -1        -            -         -1        -1
> swap_cache->freed      -         -1           -         -1        -1
> disk_swap->freed       -         -            -1        -         -1
> 
> 
> any comments are welcome.

What is the expected behaviour when we exceed memory.total_limit_in_bytes? Can't
the memrlimit controller do what you ask for?



-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL

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