Hi.
Thank you for all of your works.
Several comments are inlined.
On Mon, 2 Aug 2010 19:13:04 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
> Now, memory cgroup has an ID per cgroup and make use of it at
> - hierarchy walk,
> - swap recording.
>
> This patch is for making more use of it. The final purpose is
> to replace page_cgroup->mem_cgroup's pointer to an unsigned short.
>
> This patch caches a pointer of memcg in an array. By this, we
> don't have to call css_lookup() which requires radix-hash walk.
> This saves some amount of memory footprint at lookup memcg via id.
>
> Changelog: 20100730
> - fixed rcu_read_unlock() placement.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
> init/Kconfig | 11 +++++++++++
> mm/memcontrol.c | 48 ++++++++++++++++++++++++++++++++++--------------
> 2 files changed, 45 insertions(+), 14 deletions(-)
>
> Index: mmotm-0727/mm/memcontrol.c
> ===================================================================
> --- mmotm-0727.orig/mm/memcontrol.c
> +++ mmotm-0727/mm/memcontrol.c
> @@ -292,6 +292,30 @@ static bool move_file(void)
> &mc.to->move_charge_at_immigrate);
> }
>
> +/* 0 is unused */
> +static atomic_t mem_cgroup_num;
> +#define NR_MEMCG_GROUPS (CONFIG_MEM_CGROUP_MAX_GROUPS + 1)
> +static struct mem_cgroup *mem_cgroups[NR_MEMCG_GROUPS] __read_mostly;
> +
> +static struct mem_cgroup *id_to_memcg(unsigned short id)
> +{
> + /*
> + * This array is set to NULL when mem_cgroup is freed.
> + * IOW, there are no more references && rcu_synchronized().
> + * This lookup-caching is safe.
> + */
> + if (unlikely(!mem_cgroups[id])) {
> + struct cgroup_subsys_state *css;
> +
> + rcu_read_lock();
> + css = css_lookup(&mem_cgroup_subsys, id);
> + rcu_read_unlock();
> + if (!css)
> + return NULL;
> + mem_cgroups[id] = container_of(css, struct mem_cgroup, css);
> + }
> + return mem_cgroups[id];
> +}
id_to_memcg() seems to be called under rcu_read_lock() already, so I think
rcu_read_lock()/unlock() would be unnecessary.
> Index: mmotm-0727/init/Kconfig
> ===================================================================
> --- mmotm-0727.orig/init/Kconfig
> +++ mmotm-0727/init/Kconfig
> @@ -594,6 +594,17 @@ config CGROUP_MEM_RES_CTLR_SWAP
> Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
> size is 4096bytes, 512k per 1Gbytes of swap.
>
> +config MEM_CGROUP_MAX_GROUPS
> + int "Maximum number of memory cgroups on a system"
> + range 1 65535
> + default 8192 if 64BIT
> + default 2048 if 32BIT
> + help
> + Memory cgroup has limitation of the number of groups created.
> + Please select your favorite value. The more you allow, the more
> + memory will be consumed. This consumes vmalloc() area, so,
> + this should be small on 32bit arch.
> +
We don't use vmalloc() area in this version :)
Thanks,
Daisuke Nishimura.
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