Re: [RFC][PATCH] the proposal of improve page reclaim by throttle

[Balbir Singh]

KOSAKI Motohiro wrote:
> background
> ========================================
> current VM implementation doesn't has limit of # of parallel reclaim.
> when heavy workload, it bring to 2 bad things
>   - heavy lock contention
>   - unnecessary swap out
> 
> abount 2 month ago, KAMEZA Hiroyuki proposed the patch of page 
> reclaim throttle and explain it improve reclaim time.
> 	http://marc.info/?l=linux-mm&m=119667465917215&w=2
> 
> but unfortunately it works only memcgroup reclaim.
> Today, I implement it again for support global reclaim and mesure it.
> 

Hi, Kosaki,

It's good to keep the main reclaim code and the memory controller reclaim in
sync, so this is a nice effort.

> @@ -1456,7 +1501,7 @@ unsigned long try_to_free_mem_cgroup_pag
>  	int target_zone = gfp_zone(GFP_HIGHUSER_MOVABLE);
> 
>  	zones = NODE_DATA(numa_node_id())->node_zonelists[target_zone].zones;
> -	if (do_try_to_free_pages(zones, sc.gfp_mask, &sc))
> +	if (try_to_free_pages_throttled(zones, 0, sc.gfp_mask, &sc))
>  		return 1;
>  	return 0;
>  }
> 

try_to_free_pages_throttled checks for zone_watermark_ok(), that will not work
in the case that we are reclaiming from a cgroup which over it's limit. We need
a different check, to see if the mem_cgroup is still over it's limit or not.

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