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
> 18:03:08]:
>
>> On Mon, 16 Mar 2009 17:49:43 +0900
>> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>>
>> > On Mon, 16 Mar 2009 14:05:12 +0530
>> > Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
>>
>> > For example, shrink_slab() is not called. and this must be called.
>> >
>> > For exmaple, we may have to add
>> >  sc->call_shrink_slab
>> > flag and set it "true" at soft limit reclaim.
>> >
>> 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.


> 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.)

Anyway, we'll have to add softlimit hook to kswapd.
I think you read Kosaki's e-mail to you.
==
in global reclaim view, foreground reclaim and background reclaim's
  reclaim rate is about 1:9 typically.
==

Thanks,
-Kame

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