Re: Question about cgroup hierarchy and reducing memory limit

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

On Mon, 22 Nov 2010 19:59:41 +0300
Evgeniy Ivanov <lolkaantimat@gmail.com> wrote:

> Hello,
> 
Hi,

> I have following cgroup hierarchy:
> 
>   Root
>   /   |
> A   B
> 
> A and B have memory limits set so that it's 100% of limit set in Root.
> I want to add C to root:
> 
>   Root
>   /   |  \
> A   B  C
> 
> What is correct way to shrink limits for A and B? When they use all
> allowed memory and I try to write to their limit files I get error. 

What kinds of error ? Do you have swap ? What is the kerenel version ?

> It seems, that I can shrink their limits multiple times by 1Mb and it
> works, but looks ugly and like very dirty workaround.
> 

It's designed to allow "shrink at once" but that means release memory
and do forced-writeback. To release memory, it may have to write back
to swap. If tasks in "A" and "B" are too busy and tocuhes tons of memory
while shrinking, it may fail.

It may be a regression. Kernel version is important.

Could you show memory.stat file when you shrink "A" and "B" ?
And what happnes
# sync
# sync
# sync
# reduce memory A
# reduce memory B

one by one ?
Thanks,
-Kame

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