Re: [PATCH] memcg: rework inactive_ratio logic

[Konstantin Khlebnikov <khlebnikov-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>]

KAMEZAWA Hiroyuki wrote:
> On Wed, 15 Feb 2012 20:24:42 +0400
> Konstantin Khlebnikov<khlebnikov-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>  wrote:
>
>> This patch adds mem_cgroup->inactive_ratio calculated from hierarchical memory limit.
>> It updated at each limit change before shrinking cgroup to this new limit.
>> Ratios for all child cgroups are updated too, because parent limit can affect them.
>> Update precedure can be greatly optimized if its performance becomes the problem.
>> Inactive ratio for unlimited or huge limit does not matter, because we'll never hit it.
>>
>> At global reclaim always use global ratio from zone->inactive_ratio.
>> At mem-cgroup reclaim use inactive_ratio from target memory cgroup,
>> this is cgroup which hit its limit and cause this reclaimer invocation.
>>
>> Thus, global memory reclaimer will try to keep ratio for all lru lists in zone
>> above one mark, this guarantee that total ratio in this zone will be above too.
>> Meanwhile mem-cgroup will do the same thing for its lru lists in all zones, and
>> for all lru lists in all sub-cgroups in hierarchy.
>>
>> Also this patch removes some redundant code.
>>
>> Signed-off-by: Konstantin Khlebnikov<khlebnikov-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>
>
> Hmm, the main purpose of this patch is to remove calculation per get_scan_ratio() ?

Technically, it was preparation for "mm: unify inactive_list_is_low()" from "memory book keeping" patchset.
So, actually its main purpose is moving all active/inactive size calculation to mm/vmscan.c

Also I trying to figure out most sane logic for inactive_ratio calculation,
currently global memory reclaimer sometimes uses memcg-calculated ratio, it looks strange.

>> ---
>>   include/linux/memcontrol.h |   16 ++------
>>   mm/memcontrol.c            |   85 ++++++++++++++++++++++++--------------------
>>   mm/vmscan.c                |   82 +++++++++++++++++++++++-------------------
>>   3 files changed, 93 insertions(+), 90 deletions(-)
>>   static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
>>                                unsigned long long val)
>>   {

<cut>

>> @@ -3422,6 +3416,7 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
>>                        else
>>                                memcg->memsw_is_minimum = false;
>>                }
>> +             mem_cgroup_update_inactive_ratio(memcg, val);
>>                mutex_unlock(&set_limit_mutex);
>>
>>                if (!ret)
>> @@ -3439,6 +3434,12 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
>>        if (!ret&&  enlarge)
>>                memcg_oom_recover(memcg);
>>
>> +     if (ret) {
>> +             mutex_lock(&set_limit_mutex);
>> +             mem_cgroup_update_inactive_ratio(memcg, RESOURCE_MAX);
>> +             mutex_unlock(&set_limit_mutex);
>> +     }
>
> Why RESOUECE_MAX ?

resize was failed, so we return back normal value calculated from the current limit.
target == RESOURCE_MAX isn't clip limit: min(RESOURCE_MAX, limit) == limit

>
> Thanks,
> -Kame
>