On Sun 13-09-20 22:44:51, Waiman Long wrote:
> The mem_cgroup_get_max() function used to get memory+swap max from
> both the v1 memsw and v2 memory+swap page counters & return the maximum
> of these 2 values. This is redundant and it is more efficient to just
> get either the v1 or the v2 values depending on which one is currently
> in use.
>
> Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> ---
> mm/memcontrol.c | 20 +++++++++-----------
> 1 file changed, 9 insertions(+), 11 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 8c74f1200261..ca36bed588d1 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1633,17 +1633,15 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
> */
> unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
> {
> - unsigned long max;
> -
> - max = READ_ONCE(memcg->memory.max);
> - if (mem_cgroup_swappiness(memcg)) {
> - unsigned long memsw_max;
> - unsigned long swap_max;
> -
> - memsw_max = memcg->memsw.max;
> - swap_max = READ_ONCE(memcg->swap.max);
> - swap_max = min(swap_max, (unsigned long)total_swap_pages);
> - max = min(max + swap_max, memsw_max);
> + unsigned long max = READ_ONCE(memcg->memory.max);
> +
> + if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
> + if (mem_cgroup_swappiness(memcg))
> + max += min(READ_ONCE(memcg->swap.max),
> + (unsigned long)total_swap_pages);
> + } else { /* v1 */
> + if (mem_cgroup_swappiness(memcg))
> + max = memcg->memsw.max;
I agree that making v1 vs. v2 distinction here makes the code more
obvious. But I do not think your code is correct for v1. In a default
state it would lead to max = PAGE_COUNTER_MAX which is not something
we want, right?
instead you want
max += min(READ_ONCE(memcg->memsw.max), total_swap_pages);
> }
> return max;
> }
> --
> 2.18.1
>
--
Michal Hocko
SUSE Labs
