[Devel] Re: [PATCH 02/11] memcg: Reclaim when more than one page needed.

[David Rientjes]

On Mon, 25 Jun 2012, Glauber Costa wrote:

> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 9304db2..8e601e8 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2158,8 +2158,16 @@ enum {
>  	CHARGE_OOM_DIE,		/* the current is killed because of OOM */
>  };
>  
> +/*
> + * We need a number that is small enough to be likely to have been
> + * reclaimed even under pressure, but not too big to trigger unnecessary 

Whitespace.

> + * retries
> + */
> +#define NR_PAGES_TO_RETRY 2
> +

Should be 1 << PAGE_ALLOC_COSTLY_ORDER?  Where does this number come from?  
The changelog doesn't specify.

>  static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
> -				unsigned int nr_pages, bool oom_check)
> +				unsigned int nr_pages, unsigned int min_pages,
> +				bool oom_check)
>  {
>  	unsigned long csize = nr_pages * PAGE_SIZE;
>  	struct mem_cgroup *mem_over_limit;
> @@ -2182,18 +2190,18 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
>  	} else
>  		mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
>  	/*
> -	 * nr_pages can be either a huge page (HPAGE_PMD_NR), a batch
> -	 * of regular pages (CHARGE_BATCH), or a single regular page (1).
> -	 *
>  	 * Never reclaim on behalf of optional batching, retry with a
>  	 * single page instead.
>  	 */
> -	if (nr_pages == CHARGE_BATCH)
> +	if (nr_pages > min_pages)
>  		return CHARGE_RETRY;
>  
>  	if (!(gfp_mask & __GFP_WAIT))
>  		return CHARGE_WOULDBLOCK;
>  
> +	if (gfp_mask & __GFP_NORETRY)
> +		return CHARGE_NOMEM;
> +
>  	ret = mem_cgroup_reclaim(mem_over_limit, gfp_mask, flags);
>  	if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
>  		return CHARGE_RETRY;
> @@ -2206,7 +2214,7 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
>  	 * unlikely to succeed so close to the limit, and we fall back
>  	 * to regular pages anyway in case of failure.
>  	 */
> -	if (nr_pages == 1 && ret)
> +	if (nr_pages <= NR_PAGES_TO_RETRY && ret)
>  		return CHARGE_RETRY;
>  
>  	/*
> @@ -2341,7 +2349,8 @@ again:
>  			nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
>  		}
>  
> -		ret = mem_cgroup_do_charge(memcg, gfp_mask, batch, oom_check);
> +		ret = mem_cgroup_do_charge(memcg, gfp_mask, batch, nr_pages,
> +		    oom_check);
>  		switch (ret) {
>  		case CHARGE_OK:
>  			break;