Re: [PATCH 4/4] Memory controller soft limit reclaim on contention (v6)

["KAMEZAWA Hiroyuki" <kamezawa.hiroyu@jp.fujitsu.com>]

Balbir Singh wrote:
> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-03-16
> 20:10:41]:
>> >> At least, this check will be necessary in v7, I think.
>> >> shrink_slab() should be called.
>> >
>> > Why do you think so? So here is the design
>> >
>> > 1. If a cgroup was using over its soft limit, we believe that this
>> >    cgroup created overall memory contention and caused the page
>> >    reclaimer to get activated.
>> This assumption is wrong, see below.
>>
>> >    If we can solve the situation by
>> >    reclaiming from this cgroup, why do we need to invoke shrink_slab?
>> >
>> No,
>> IIUC, in big server, inode, dentry cache etc....can occupy Gigabytes
>> of memory even if 99% of them are not used.
>>
>> By shrink_slab(), we can reclaim unused but cached slabs and make
>> the kernel more healthy.
>>
>
> But that is not the job of the soft limit reclaimer.. Yes if no groups
> are over their soft limit, the regular action will take place.
>
Oh, yes, it's not job of memcg but it's job of memory management.


>>
>> > If the concern is that we are not following the traditional reclaim,
>> > soft limit reclaim can be followed by unconditional reclaim, but I
>> > believe this is not necessary. Remember, we wake up kswapd that will
>> > call shrink_slab if needed.
>> kswapd doesn't call shrink_slab() when zone->free is enough.
>> (when direct recail did good jobs.)
>>
>
> If zone->free is high why do we need shrink_slab()? The other way
> of asking it is, why does the soft limit reclaimer need to call
> shrink_slab(), when its job is to reclaim memory from cgroups above
> their soft limits.
>
Why do you consider that softlimit is called more than necessary
if shrink_slab() is never called ?

Thanks,
-Kame


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