[Devel] Re: [PATCH v2 01/11] memcg: Make it possible to use the stock for more than one page.

[Michal Hocko]

On Thu 09-08-12 17:01:09, Glauber Costa wrote:
> From: Suleiman Souhlal <ssouhlal at FreeBSD.org>
> 
> We currently have a percpu stock cache scheme that charges one page at a
> time from memcg->res, the user counter. When the kernel memory
> controller comes into play, we'll need to charge more than that.
> 
> This is because kernel memory allocations will also draw from the user
> counter, and can be bigger than a single page, as it is the case with
> the stack (usually 2 pages) or some higher order slabs.
> 
> [ glommer at parallels.com: added a changelog ]
> 
> Signed-off-by: Suleiman Souhlal <suleiman at google.com>
> Signed-off-by: Glauber Costa <glommer at parallels.com>
> Acked-by: David Rientjes <rientjes at google.com>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>

Acked-by: Michal Hocko <mhocko at suse.cz>

> ---
>  mm/memcontrol.c | 28 ++++++++++++++++++----------
>  1 file changed, 18 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 95162c9..bc7bfa7 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2096,20 +2096,28 @@ struct memcg_stock_pcp {
>  static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
>  static DEFINE_MUTEX(percpu_charge_mutex);
>  
> -/*
> - * Try to consume stocked charge on this cpu. If success, one page is consumed
> - * from local stock and true is returned. If the stock is 0 or charges from a
> - * cgroup which is not current target, returns false. This stock will be
> - * refilled.
> +/**
> + * consume_stock: Try to consume stocked charge on this cpu.
> + * @memcg: memcg to consume from.
> + * @nr_pages: how many pages to charge.
> + *
> + * The charges will only happen if @memcg matches the current cpu's memcg
> + * stock, and at least @nr_pages are available in that stock.  Failure to
> + * service an allocation will refill the stock.
> + *
> + * returns true if succesfull, false otherwise.
>   */
> -static bool consume_stock(struct mem_cgroup *memcg)
> +static bool consume_stock(struct mem_cgroup *memcg, int nr_pages)
>  {
>  	struct memcg_stock_pcp *stock;
>  	bool ret = true;
>  
> +	if (nr_pages > CHARGE_BATCH)
> +		return false;
> +
>  	stock = &get_cpu_var(memcg_stock);
> -	if (memcg == stock->cached && stock->nr_pages)
> -		stock->nr_pages--;
> +	if (memcg == stock->cached && stock->nr_pages >= nr_pages)
> +		stock->nr_pages -= nr_pages;
>  	else /* need to call res_counter_charge */
>  		ret = false;
>  	put_cpu_var(memcg_stock);
> @@ -2408,7 +2416,7 @@ again:
>  		VM_BUG_ON(css_is_removed(&memcg->css));
>  		if (mem_cgroup_is_root(memcg))
>  			goto done;
> -		if (nr_pages == 1 && consume_stock(memcg))
> +		if (consume_stock(memcg, nr_pages))
>  			goto done;
>  		css_get(&memcg->css);
>  	} else {
> @@ -2433,7 +2441,7 @@ again:
>  			rcu_read_unlock();
>  			goto done;
>  		}
> -		if (nr_pages == 1 && consume_stock(memcg)) {
> +		if (consume_stock(memcg, nr_pages)) {
>  			/*
>  			 * It seems dagerous to access memcg without css_get().
>  			 * But considering how consume_stok works, it's not
> -- 
> 1.7.11.2
> 
> --
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-- 
Michal Hocko
SUSE Labs