2014-12-28 18:48:04

by Johannes Weiner

Subject: [patch] mm: memcontrol: switch soft limit default back to infinity

3e32cb2e0a12 ("mm: memcontrol: lockless page counters") accidentally
switched the soft limit default from infinity to zero, which turns all
memcgs with even a single page into soft limit excessors and engages
soft limit reclaim on all of them during global memory pressure. This
makes global reclaim generally more aggressive, but also inverts the
meaning of existing soft limit configurations where unset soft limits
are usually more generous than set ones.

Signed-off-by: Johannes Weiner <[email protected]>
---
mm/memcontrol.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ef91e856c7e4..b7104a55ae64 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4679,6 +4679,7 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
if (parent_css == NULL) {
root_mem_cgroup = memcg;
page_counter_init(&memcg->memory, NULL);
+ memcg->soft_limit = PAGE_COUNTER_MAX;
page_counter_init(&memcg->memsw, NULL);
page_counter_init(&memcg->kmem, NULL);
}
@@ -4724,6 +4725,7 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)

if (parent->use_hierarchy) {
page_counter_init(&memcg->memory, &parent->memory);
+ memcg->soft_limit = PAGE_COUNTER_MAX;
page_counter_init(&memcg->memsw, &parent->memsw);
page_counter_init(&memcg->kmem, &parent->kmem);

@@ -4733,6 +4735,7 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
*/
} else {
page_counter_init(&memcg->memory, NULL);
+ memcg->soft_limit = PAGE_COUNTER_MAX;
page_counter_init(&memcg->memsw, NULL);
page_counter_init(&memcg->kmem, NULL);
/*
@@ -4807,7 +4810,7 @@ static void mem_cgroup_css_reset(struct cgroup_subsys_state *css)
mem_cgroup_resize_limit(memcg, PAGE_COUNTER_MAX);
mem_cgroup_resize_memsw_limit(memcg, PAGE_COUNTER_MAX);
memcg_update_kmem_limit(memcg, PAGE_COUNTER_MAX);
- memcg->soft_limit = 0;
+ memcg->soft_limit = PAGE_COUNTER_MAX;
}

#ifdef CONFIG_MMU
--
2.2.0

2014-12-29 08:22:36

by Michal Hocko

Subject: Re: [patch] mm: memcontrol: switch soft limit default back to infinity

On Sun 28-12-14 13:47:48, Johannes Weiner wrote:
> 3e32cb2e0a12 ("mm: memcontrol: lockless page counters") accidentally
> switched the soft limit default from infinity to zero, which turns all

Should have noticed that during the review :/

> memcgs with even a single page into soft limit excessors and engages
> soft limit reclaim on all of them during global memory pressure. This
> makes global reclaim generally more aggressive, but also inverts the
> meaning of existing soft limit configurations where unset soft limits
> are usually more generous than set ones.
>
> Signed-off-by: Johannes Weiner <[email protected]>

Acked-by: Michal Hocko <[email protected]>

Thanks!

> ---
> mm/memcontrol.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index ef91e856c7e4..b7104a55ae64 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4679,6 +4679,7 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
> if (parent_css == NULL) {
> root_mem_cgroup = memcg;
> page_counter_init(&memcg->memory, NULL);
> + memcg->soft_limit = PAGE_COUNTER_MAX;
> page_counter_init(&memcg->memsw, NULL);
> page_counter_init(&memcg->kmem, NULL);
> }
> @@ -4724,6 +4725,7 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
>
> if (parent->use_hierarchy) {
> page_counter_init(&memcg->memory, &parent->memory);
> + memcg->soft_limit = PAGE_COUNTER_MAX;
> page_counter_init(&memcg->memsw, &parent->memsw);
> page_counter_init(&memcg->kmem, &parent->kmem);
>
> @@ -4733,6 +4735,7 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
> */
> } else {
> page_counter_init(&memcg->memory, NULL);
> + memcg->soft_limit = PAGE_COUNTER_MAX;
> page_counter_init(&memcg->memsw, NULL);
> page_counter_init(&memcg->kmem, NULL);
> /*
> @@ -4807,7 +4810,7 @@ static void mem_cgroup_css_reset(struct cgroup_subsys_state *css)
> mem_cgroup_resize_limit(memcg, PAGE_COUNTER_MAX);
> mem_cgroup_resize_memsw_limit(memcg, PAGE_COUNTER_MAX);
> memcg_update_kmem_limit(memcg, PAGE_COUNTER_MAX);
> - memcg->soft_limit = 0;
> + memcg->soft_limit = PAGE_COUNTER_MAX;
> }
>
> #ifdef CONFIG_MMU
> --
> 2.2.0
>

--
Michal Hocko
SUSE Labs

2014-12-29 08:43:14

by Vladimir Davydov

Subject: Re: [patch] mm: memcontrol: switch soft limit default back to infinity

On Sun, Dec 28, 2014 at 01:47:48PM -0500, Johannes Weiner wrote:
> 3e32cb2e0a12 ("mm: memcontrol: lockless page counters") accidentally
> switched the soft limit default from infinity to zero, which turns all
> memcgs with even a single page into soft limit excessors and engages
> soft limit reclaim on all of them during global memory pressure. This
> makes global reclaim generally more aggressive, but also inverts the
> meaning of existing soft limit configurations where unset soft limits
> are usually more generous than set ones.
>
> Signed-off-by: Johannes Weiner <[email protected]>

Overlooked that :-/

Acked-by: Vladimir Davydov <[email protected]>