On Fri 27-12-19 07:43:52, Yafang Shao wrote:
> There are some members in struct mem_group can be either 0(false) or
> 1(true), so we can define them using bit field to reduce size. With this
> patch, the size of struct mem_cgroup can be reduced by 64 bytes in theory,
> but as there're some MEMCG_PADDING()s, the real number may be different,
> which is relate with the cacheline size. Anyway, this patch could reduce
> the size of struct mem_cgroup more or less.
Pahole says
/* size: 2496, cachelines: 39, members: 48 */
/* sum members: 2364, holes: 8, sum holes: 108 */
/* padding: 24 */
/* forced alignments: 3, forced holes: 2, sum forced holes: 88 */
after the change
/* size: 2496, cachelines: 39, members: 48 */
/* sum members: 2352, holes: 7, sum holes: 108 */
/* sum bitfield members: 6 bits, bit holes: 1, sum bit holes: 26 bits */
/* padding: 32 */
/* forced alignments: 3, forced holes: 2, sum forced holes: 88 */
so exactly 0 change. I do not think this reshuffling is worth it.
>
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> Cc: Roman Gushchin <guro@xxxxxx>
> ---
> include/linux/memcontrol.h | 21 ++++++++++++---------
> 1 file changed, 12 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index a7a0a1a5..f68a9ef 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -229,20 +229,26 @@ struct mem_cgroup {
> /*
> * Should the accounting and control be hierarchical, per subtree?
> */
> - bool use_hierarchy;
> + unsigned int use_hierarchy : 1;
> +
> + /* Legacy tcp memory accounting */
> + unsigned int tcpmem_active : 1;
> + unsigned int tcpmem_pressure : 1;
>
> /*
> * Should the OOM killer kill all belonging tasks, had it kill one?
> */
> - bool oom_group;
> + unsigned int oom_group : 1;
>
> /* protected by memcg_oom_lock */
> - bool oom_lock;
> - int under_oom;
> + unsigned int oom_lock : 1;
>
> - int swappiness;
> /* OOM-Killer disable */
> - int oom_kill_disable;
> + unsigned int oom_kill_disable : 1;
> +
> + int under_oom;
> +
> + int swappiness;
>
> /* memory.events and memory.events.local */
> struct cgroup_file events_file;
> @@ -297,9 +303,6 @@ struct mem_cgroup {
>
> unsigned long socket_pressure;
>
> - /* Legacy tcp memory accounting */
> - bool tcpmem_active;
> - int tcpmem_pressure;
>
> #ifdef CONFIG_MEMCG_KMEM
> /* Index in the kmem_cache->memcg_params.memcg_caches array */
> --
> 1.8.3.1
--
Michal Hocko
SUSE Labs
