Re: [PATCH 2/2] memcg: do not use vmalloc for mem_cgroup allocations

[Michal Hocko <mhocko@suse.cz>]

On Sat 14-12-13 12:15:34, Vladimir Davydov wrote:
> The vmalloc was introduced by patch 333279 ("memcgroup: use vmalloc for
> mem_cgroup allocation"), because at that time MAX_NUMNODES was used for
> defining the per-node array in the mem_cgroup structure so that the
> structure could be huge even if the system had the only NUMA node.
> 
> The situation was significantly improved by patch 45cf7e ("memcg: reduce
> the size of struct memcg 244-fold"), which made the size of the
> mem_cgroup structure calculated dynamically depending on the real number
> of NUMA nodes installed on the system (nr_node_ids), so now there is no
> point in using vmalloc here: the structure is allocated rarely and on
> most systems its size is about 1K.
> 
> Personally I'd like to remove this vmalloc, because I'm considering
> using wait_on_bit() on mem_cgroup::kmem_account_flags in the kmemcg
> shrinkers implementation, which is impossible on vmalloc'd areas.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
> Cc: Michal Hocko <mhocko@suse.cz>
> Cc: Glauber Costa <glommer@openvz.org>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Balbir Singh <bsingharora@gmail.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

yes this makes sense to me even without wait_on_bit part.
Maybe I would just merge it with 1/2.

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

Thanks!
> ---
>  mm/memcontrol.c |   28 ++++++----------------------
>  1 file changed, 6 insertions(+), 22 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 7f1a356..205eb7b 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -48,7 +48,6 @@
>  #include <linux/sort.h>
>  #include <linux/fs.h>
>  #include <linux/seq_file.h>
> -#include <linux/vmalloc.h>
>  #include <linux/vmpressure.h>
>  #include <linux/mm_inline.h>
>  #include <linux/page_cgroup.h>
> @@ -335,12 +334,6 @@ struct mem_cgroup {
>  	/* WARNING: nodeinfo must be the last member here */
>  };
>  
> -static size_t memcg_size(void)
> -{
> -	return sizeof(struct mem_cgroup) +
> -		nr_node_ids * sizeof(struct mem_cgroup_per_node *);
> -}
> -
>  /* internal only representation about the status of kmem accounting. */
>  enum {
>  	KMEM_ACCOUNTED_ACTIVE = 0, /* accounted by this cgroup itself */
> @@ -6139,14 +6132,12 @@ static void free_mem_cgroup_per_zone_info(struct mem_cgroup *memcg, int node)
>  static struct mem_cgroup *mem_cgroup_alloc(void)
>  {
>  	struct mem_cgroup *memcg;
> -	size_t size = memcg_size();
> +	size_t size;
>  
> -	/* Can be very big if nr_node_ids is very big */
> -	if (size < PAGE_SIZE)
> -		memcg = kzalloc(size, GFP_KERNEL);
> -	else
> -		memcg = vzalloc(size);
> +	size = sizeof(struct mem_cgroup);
> +	size += nr_node_ids * sizeof(struct mem_cgroup_per_node *);
>  
> +	memcg = kzalloc(size, GFP_KERNEL);
>  	if (!memcg)
>  		return NULL;
>  
> @@ -6157,10 +6148,7 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
>  	return memcg;
>  
>  out_free:
> -	if (size < PAGE_SIZE)
> -		kfree(memcg);
> -	else
> -		vfree(memcg);
> +	kfree(memcg);
>  	return NULL;
>  }
>  
> @@ -6178,7 +6166,6 @@ out_free:
>  static void __mem_cgroup_free(struct mem_cgroup *memcg)
>  {
>  	int node;
> -	size_t size = memcg_size();
>  
>  	mem_cgroup_remove_from_trees(memcg);
>  
> @@ -6199,10 +6186,7 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg)
>  	 * the cgroup_lock.
>  	 */
>  	disarm_static_keys(memcg);
> -	if (size < PAGE_SIZE)
> -		kfree(memcg);
> -	else
> -		vfree(memcg);
> +	kfree(memcg);
>  }
>  
>  /*
> -- 
> 1.7.10.4
> 

-- 
Michal Hocko
SUSE Labs

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