On Sun 13-09-20 22:44:52, Waiman Long wrote:
> The swap page counter is v2 only while memsw is v1 only. As v1 and v2
> controllers cannot be active at the same time, there is no point to keep
> both swap and memsw page counters in mem_cgroup. The previous patch has
> made sure that memsw page counter is updated and accessed only when in
> v1 code paths. So it is now safe to alias the v1 memsw page counter to v2
> swap page counter. This saves 14 long's in the size of mem_cgroup. This
> is a saving of 112 bytes for 64-bit archs.
I didn't realize that page_counter is so large.
> While at it, also document which page counters are used in v1 and/or v2.
>
> Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> include/linux/memcontrol.h | 13 ++++++++-----
> mm/memcontrol.c | 3 ---
> 2 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index d0b036123c6a..6ef4a552e09d 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -215,13 +215,16 @@ struct mem_cgroup {
> struct mem_cgroup_id id;
>
> /* Accounted resources */
> - struct page_counter memory;
> - struct page_counter swap;
> + struct page_counter memory; /* Both v1 & v2 */
> +
> + union {
> + struct page_counter swap; /* v2 only */
> + struct page_counter memsw; /* v1 only */
> + };
>
> /* Legacy consumer-oriented counters */
> - struct page_counter memsw;
> - struct page_counter kmem;
> - struct page_counter tcpmem;
> + struct page_counter kmem; /* v1 only */
> + struct page_counter tcpmem; /* v1 only */
>
> /* Range enforcement for interrupt charges */
> struct work_struct high_work;
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index ca36bed588d1..188901f3a3db 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5281,13 +5281,11 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
> memcg->use_hierarchy = true;
> page_counter_init(&memcg->memory, &parent->memory);
> page_counter_init(&memcg->swap, &parent->swap);
> - page_counter_init(&memcg->memsw, &parent->memsw);
> page_counter_init(&memcg->kmem, &parent->kmem);
> page_counter_init(&memcg->tcpmem, &parent->tcpmem);
> } else {
> page_counter_init(&memcg->memory, NULL);
> page_counter_init(&memcg->swap, NULL);
> - page_counter_init(&memcg->memsw, NULL);
> page_counter_init(&memcg->kmem, NULL);
> page_counter_init(&memcg->tcpmem, NULL);
> /*
> @@ -5416,7 +5414,6 @@ static void mem_cgroup_css_reset(struct cgroup_subsys_state *css)
>
> page_counter_set_max(&memcg->memory, PAGE_COUNTER_MAX);
> page_counter_set_max(&memcg->swap, PAGE_COUNTER_MAX);
> - page_counter_set_max(&memcg->memsw, PAGE_COUNTER_MAX);
> page_counter_set_max(&memcg->kmem, PAGE_COUNTER_MAX);
> page_counter_set_max(&memcg->tcpmem, PAGE_COUNTER_MAX);
> page_counter_set_min(&memcg->memory, 0);
> --
> 2.18.1
--
Michal Hocko
SUSE Labs
