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

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

[Johannes Weiner]

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 <hannes@cmpxchg.org>
---
 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

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

[Michal Hocko]

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 <hannes@cmpxchg.org>

Acked-by: Michal Hocko <mhocko@suse.cz>

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

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

[Vladimir Davydov]

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 <hannes@cmpxchg.org>

Overlooked that :-/

Acked-by: Vladimir Davydov <vdavydov@parallels.com>