Re: [PATCH -mm] slab: use cgroup ino for naming per memcg caches

Andrew Morton
2015-04-07T20:38:19Z

On Tue, 7 Apr 2015 16:53:18 +0300 Vladimir Davydov <vdavydov@parallels.com> wrote:

> The name of a per memcg kmem cache consists of three parts: the global
> kmem cache name, the cgroup name, and the css id. The latter is used to
> guarantee cache name uniqueness.
>
> Since css ids are opaque to the userspace, in general it is impossible
> to find a cache's owner cgroup given its name: there might be several
> same-named cgroups with different parents so that their caches' names
> will only differ by css id. Looking up the owner cgroup by a cache name,
> however, could be useful for debugging. For instance, the cache name is
> dumped to dmesg on a slab allocation failure. Another example is
> /sys/kernel/slab, which exports some extra info/tunables for SLUB caches

/proc/sys/kernel/slab?

> referring to them by name.
>
> This patch substitutes the css id with cgroup inode number, which, just
> like css id, is reserved until css free, so that the cache names are
> still guaranteed to be unique, but, in contrast to css id, it can be
> easily obtained from userspace.
>
> ...
>
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -478,7 +478,7 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,
> struct kmem_cache *root_cache)
> {
> static char memcg_name_buf[NAME_MAX + 1]; /* protected by slab_mutex */
> - struct cgroup_subsys_state *css = mem_cgroup_css(memcg);
> + struct cgroup *cgroup;
> struct memcg_cache_array *arr;
> struct kmem_cache *s = NULL;
> char *cache_name;
> @@ -508,9 +508,10 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,
> if (arr->entries[idx])
> goto out_unlock;
>
> - cgroup_name(css->cgroup, memcg_name_buf, sizeof(memcg_name_buf));
> - cache_name = kasprintf(GFP_KERNEL, "%s(%d:%s)", root_cache->name,
> - css->id, memcg_name_buf);
> + cgroup = mem_cgroup_css(memcg)->cgroup;
> + cgroup_name(cgroup, memcg_name_buf, sizeof(memcg_name_buf));
> + cache_name = kasprintf(GFP_KERNEL, "%s(%lu:%s)", root_cache->name,
> + (unsigned long)cgroup_ino(cgroup), memcg_name_buf);
> if (!cache_name)
> goto out_unlock;

Is this interface documented anywhere?