[Devel] Re: [PATCH v7 1/2] Always free struct memcg through schedule_work()

[Michal Hocko]

On Fri 25-05-12 13:32:07, Glauber Costa wrote:
> Right now we free struct memcg with kfree right after a
> rcu grace period, but defer it if we need to use vfree() to get
> rid of that memory area. We do that by need, because we need vfree
> to be called in a process context.
> 
> This patch unifies this behavior, by ensuring that even kfree will
> happen in a separate thread. The goal is to have a stable place to
> call the upcoming jump label destruction function outside the realm
> of the complicated and quite far-reaching cgroup lock (that can't be
> held when calling neither the cpu_hotplug.lock nor the jump_label_mutex)
> 
> Signed-off-by: Glauber Costa <glommer at parallels.com>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>

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

Just one comment below

> CC: Tejun Heo <tj at kernel.org>
> CC: Li Zefan <lizefan at huawei.com>
> CC: Johannes Weiner <hannes at cmpxchg.org>
> CC: Michal Hocko <mhocko at suse.cz>
> CC: Andrew Morton <akpm at linux-foundation.org>
> ---
>  mm/memcontrol.c |   24 +++++++++++++-----------
>  1 files changed, 13 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 932a734..0b4b4c8 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
[...]
> @@ -4826,23 +4826,28 @@ out_free:
>  }
>  
>  /*
> - * Helpers for freeing a vzalloc()ed mem_cgroup by RCU,
> + * Helpers for freeing a kmalloc()ed/vzalloc()ed mem_cgroup by RCU,
>   * but in process context.  The work_freeing structure is overlaid
>   * on the rcu_freeing structure, which itself is overlaid on memsw.
>   */
> -static void vfree_work(struct work_struct *work)
> +static void free_work(struct work_struct *work)
>  {
>  	struct mem_cgroup *memcg;
> +	int size = sizeof(struct mem_cgroup);
>  
>  	memcg = container_of(work, struct mem_cgroup, work_freeing);
> -	vfree(memcg);
> +	if (size < PAGE_SIZE)

What about
	if (is_vmalloc_addr(memcg)) 
> +		kfree(memcg);
> +	else
> +		vfree(memcg);
>  }

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic