[PATCH] memcg: simplify unreclaimable groups handling in soft limit reclaim

[PATCH] memcg: simplify unreclaimable groups handling in soft limit reclaim

[Vladimir Davydov]

If we fail to reclaim anything from a cgroup during a soft reclaim pass
we want to get the next largest cgroup exceeding its soft limit. To
achieve this, we should obviously remove the current group from the tree
and then pick the largest group. Currently we have a weird loop instead.
Let's simplify it.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
---
 mm/memcontrol.c |   26 ++++----------------------
 1 file changed, 4 insertions(+), 22 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e957f0c80c6e..53393e27ff03 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3507,34 +3507,16 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 		nr_reclaimed += reclaimed;
 		*total_scanned += nr_scanned;
 		spin_lock_irq(&mctz->lock);
+		__mem_cgroup_remove_exceeded(mz, mctz);
 
 		/*
 		 * If we failed to reclaim anything from this memory cgroup
 		 * it is time to move on to the next cgroup
 		 */
 		next_mz = NULL;
-		if (!reclaimed) {
-			do {
-				/*
-				 * Loop until we find yet another one.
-				 *
-				 * By the time we get the soft_limit lock
-				 * again, someone might have aded the
-				 * group back on the RB tree. Iterate to
-				 * make sure we get a different mem.
-				 * mem_cgroup_largest_soft_limit_node returns
-				 * NULL if no other cgroup is present on
-				 * the tree
-				 */
-				next_mz =
-				__mem_cgroup_largest_soft_limit_node(mctz);
-				if (next_mz == mz)
-					css_put(&next_mz->memcg->css);
-				else /* next_mz == NULL or other memcg */
-					break;
-			} while (1);
-		}
-		__mem_cgroup_remove_exceeded(mz, mctz);
+		if (!reclaimed)
+			next_mz = __mem_cgroup_largest_soft_limit_node(mctz);
+
 		excess = soft_limit_excess(mz->memcg);
 		/*
 		 * One school of thought says that we should not add
-- 
1.7.10.4

Re: [PATCH] memcg: simplify unreclaimable groups handling in soft limit reclaim

[Johannes Weiner]

On Mon, Oct 20, 2014 at 07:55:54PM +0400, Vladimir Davydov wrote:
> If we fail to reclaim anything from a cgroup during a soft reclaim pass
> we want to get the next largest cgroup exceeding its soft limit. To
> achieve this, we should obviously remove the current group from the tree
> and then pick the largest group. Currently we have a weird loop instead.
> Let's simplify it.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>

I wonder if there will be anything left once we removed all that which
is pointless and the unnecessary from the memcg code.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Re: [PATCH] memcg: simplify unreclaimable groups handling in soft limit reclaim

[Michal Hocko]

On Mon 20-10-14 19:55:54, Vladimir Davydov wrote:
> If we fail to reclaim anything from a cgroup during a soft reclaim pass
> we want to get the next largest cgroup exceeding its soft limit. To
> achieve this, we should obviously remove the current group from the tree
> and then pick the largest group. Currently we have a weird loop instead.
> Let's simplify it.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>

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

> ---
>  mm/memcontrol.c |   26 ++++----------------------
>  1 file changed, 4 insertions(+), 22 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e957f0c80c6e..53393e27ff03 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3507,34 +3507,16 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
>  		nr_reclaimed += reclaimed;
>  		*total_scanned += nr_scanned;
>  		spin_lock_irq(&mctz->lock);
> +		__mem_cgroup_remove_exceeded(mz, mctz);
>  
>  		/*
>  		 * If we failed to reclaim anything from this memory cgroup
>  		 * it is time to move on to the next cgroup
>  		 */
>  		next_mz = NULL;
> -		if (!reclaimed) {
> -			do {
> -				/*
> -				 * Loop until we find yet another one.
> -				 *
> -				 * By the time we get the soft_limit lock
> -				 * again, someone might have aded the
> -				 * group back on the RB tree. Iterate to
> -				 * make sure we get a different mem.
> -				 * mem_cgroup_largest_soft_limit_node returns
> -				 * NULL if no other cgroup is present on
> -				 * the tree
> -				 */
> -				next_mz =
> -				__mem_cgroup_largest_soft_limit_node(mctz);
> -				if (next_mz == mz)
> -					css_put(&next_mz->memcg->css);
> -				else /* next_mz == NULL or other memcg */
> -					break;
> -			} while (1);
> -		}
> -		__mem_cgroup_remove_exceeded(mz, mctz);
> +		if (!reclaimed)
> +			next_mz = __mem_cgroup_largest_soft_limit_node(mctz);
> +
>  		excess = soft_limit_excess(mz->memcg);
>  		/*
>  		 * One school of thought says that we should not add
> -- 
> 1.7.10.4
> 

-- 
Michal Hocko
SUSE Labs