[PATCH 3/5] mm: memcg detect no memcgs above softlimit under zone reclaim.

[PATCH 3/5] mm: memcg detect no memcgs above softlimit under zone reclaim.

[Ying Han]

In memcg kernel, cgroup under its softlimit is not targeted under global
reclaim. It could be possible that all memcgs are under their softlimit for
a particular zone. If that is the case, the current implementation will
burn extra cpu cycles without making forward progress.

The idea is from LSF discussion where we detect it after the first round of
scanning and restart the reclaim by not looking at softlimit at all. This
allows us to make forward progress on shrink_zone().

Signed-off-by: Ying Han <yinghan@google.com>
---
 mm/vmscan.c |   18 ++++++++++++++++--
 1 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0560783..5d036f5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2142,6 +2142,10 @@ static void shrink_zone(int priority, struct zone *zone,
 		.priority = priority,
 	};
 	struct mem_cgroup *memcg;
+	bool over_softlimit, ignore_softlimit = false;
+
+restart:
+	over_softlimit = false;
 
 	memcg = mem_cgroup_iter(root, NULL, &reclaim);
 	do {
@@ -2163,9 +2167,14 @@ static void shrink_zone(int priority, struct zone *zone,
 		 * we have to reclaim under softlimit instead of burning more
 		 * cpu cycles.
 		 */
-		if (!global_reclaim(sc) || priority < DEF_PRIORITY - 2 ||
-				should_reclaim_mem_cgroup(memcg))
+		if (ignore_softlimit || !global_reclaim(sc) ||
+				priority < DEF_PRIORITY - 2 ||
+				should_reclaim_mem_cgroup(memcg)) {
 			shrink_mem_cgroup_zone(priority, &mz, sc);
+
+			over_softlimit = true;
+		}
+
 		/*
 		 * Limit reclaim has historically picked one memcg and
 		 * scanned it with decreasing priority levels until
@@ -2182,6 +2191,11 @@ static void shrink_zone(int priority, struct zone *zone,
 		}
 		memcg = mem_cgroup_iter(root, memcg, &reclaim);
 	} while (memcg);
+
+	if (!over_softlimit) {
+		ignore_softlimit = true;
+		goto restart;
+	}
 }
 
 /* Returns true if compaction should go ahead for a high-order request */
-- 
1.7.7.3

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Re: [PATCH 3/5] mm: memcg detect no memcgs above softlimit under zone reclaim.

[Kamezawa Hiroyuki]

(2012/06/07 3:23), Ying Han wrote:
> In memcg kernel, cgroup under its softlimit is not targeted under global
> reclaim. It could be possible that all memcgs are under their softlimit for
> a particular zone. If that is the case, the current implementation will
> burn extra cpu cycles without making forward progress.
> 
> The idea is from LSF discussion where we detect it after the first round of
> scanning and restart the reclaim by not looking at softlimit at all. This
> allows us to make forward progress on shrink_zone().
> 
> Signed-off-by: Ying Han<yinghan@google.com>

Hm, how about adding sc->ignore_softlimit and preserve the result among priority loops ?

Is it better to check 'ignore_softlimit' at every priority updates ?

Thanks,
-Kame

> ---
>   mm/vmscan.c |   18 ++++++++++++++++--
>   1 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 0560783..5d036f5 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2142,6 +2142,10 @@ static void shrink_zone(int priority, struct zone *zone,
>   		.priority = priority,
>   	};
>   	struct mem_cgroup *memcg;
> +	bool over_softlimit, ignore_softlimit = false;
> +
> +restart:
> +	over_softlimit = false;
> 
>   	memcg = mem_cgroup_iter(root, NULL,&reclaim);
>   	do {
> @@ -2163,9 +2167,14 @@ static void shrink_zone(int priority, struct zone *zone,
>   		 * we have to reclaim under softlimit instead of burning more
>   		 * cpu cycles.
>   		 */
> -		if (!global_reclaim(sc) || priority<  DEF_PRIORITY - 2 ||
> -				should_reclaim_mem_cgroup(memcg))
> +		if (ignore_softlimit || !global_reclaim(sc) ||
> +				priority<  DEF_PRIORITY - 2 ||
> +				should_reclaim_mem_cgroup(memcg)) {
>   			shrink_mem_cgroup_zone(priority,&mz, sc);
> +
> +			over_softlimit = true;
> +		}
> +
>   		/*
>   		 * Limit reclaim has historically picked one memcg and
>   		 * scanned it with decreasing priority levels until
> @@ -2182,6 +2191,11 @@ static void shrink_zone(int priority, struct zone *zone,
>   		}
>   		memcg = mem_cgroup_iter(root, memcg,&reclaim);
>   	} while (memcg);
> +
> +	if (!over_softlimit) {
> +		ignore_softlimit = true;
> +		goto restart;
> +	}
>   }
> 
>   /* Returns true if compaction should go ahead for a high-order request */


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Re: [PATCH 3/5] mm: memcg detect no memcgs above softlimit under zone reclaim.

[Ying Han]

On Sun, Jun 17, 2012 at 7:54 PM, Kamezawa Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> (2012/06/07 3:23), Ying Han wrote:
>> In memcg kernel, cgroup under its softlimit is not targeted under global
>> reclaim. It could be possible that all memcgs are under their softlimit for
>> a particular zone. If that is the case, the current implementation will
>> burn extra cpu cycles without making forward progress.
>>
>> The idea is from LSF discussion where we detect it after the first round of
>> scanning and restart the reclaim by not looking at softlimit at all. This
>> allows us to make forward progress on shrink_zone().
>>
>> Signed-off-by: Ying Han<yinghan@google.com>
>
> Hm, how about adding sc->ignore_softlimit and preserve the result among priority loops ?
>
> Is it better to check 'ignore_softlimit' at every priority updates ?

The softlimit and usage_in_bytes could change on each memcg, and we
might have to check the ignore_softlimit on each priority loop.

--Ying

>
> Thanks,
> -Kame
>
>> ---
>>   mm/vmscan.c |   18 ++++++++++++++++--
>>   1 files changed, 16 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 0560783..5d036f5 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -2142,6 +2142,10 @@ static void shrink_zone(int priority, struct zone *zone,
>>               .priority = priority,
>>       };
>>       struct mem_cgroup *memcg;
>> +     bool over_softlimit, ignore_softlimit = false;
>> +
>> +restart:
>> +     over_softlimit = false;
>>
>>       memcg = mem_cgroup_iter(root, NULL,&reclaim);
>>       do {
>> @@ -2163,9 +2167,14 @@ static void shrink_zone(int priority, struct zone *zone,
>>                * we have to reclaim under softlimit instead of burning more
>>                * cpu cycles.
>>                */
>> -             if (!global_reclaim(sc) || priority<  DEF_PRIORITY - 2 ||
>> -                             should_reclaim_mem_cgroup(memcg))
>> +             if (ignore_softlimit || !global_reclaim(sc) ||
>> +                             priority<  DEF_PRIORITY - 2 ||
>> +                             should_reclaim_mem_cgroup(memcg)) {
>>                       shrink_mem_cgroup_zone(priority,&mz, sc);
>> +
>> +                     over_softlimit = true;
>> +             }
>> +
>>               /*
>>                * Limit reclaim has historically picked one memcg and
>>                * scanned it with decreasing priority levels until
>> @@ -2182,6 +2191,11 @@ static void shrink_zone(int priority, struct zone *zone,
>>               }
>>               memcg = mem_cgroup_iter(root, memcg,&reclaim);
>>       } while (memcg);
>> +
>> +     if (!over_softlimit) {
>> +             ignore_softlimit = true;
>> +             goto restart;
>> +     }
>>   }
>>
>>   /* Returns true if compaction should go ahead for a high-order request */
>
>

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