Re: [RFC] [PATCH 3/4] Reclaim from groups over their soft limit under memory pressure

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

On Fri, 15 Feb 2008 09:55:20 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> Paul Menage wrote:
> > On Thu, Feb 14, 2008 at 1:16 AM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> >>  > Probably backgound-reclaim patch will be able to help this soft-limit situation,
> >>  > if a daemon can know it should reclaim or not.
> >>  >
> >>
> >>  Yes, I agree. I might just need to schedule the daemon under memory pressure.
> >>
> > 
> > Can we also have a way to trigger a one-off reclaim (of a configurable
> > magnitude) from userspace? Having a background daemon doing it may be
> > fine as a default, but there will be cases when a userspace machine
> > manager knows better than the kernel how frequently/hard to try to
> > reclaim on a given cgroup.
> > 
> > Paul
> 
> We have that capability, but we cannot specify how much to reclaim.
> There is a force_empty file that when written to, tries to reclaim all pages
> from the cgroup. Depending on the need, it can be extended so that the number of
> pages to be reclaimed can be specified.
> 
Note:
Now, force_empty doesn't try to free memory but just drops charges.

We can free memory by just making memory.limit to smaller number.
(This may cause OOM. If we added high-low watermark, making memory.high smaller
 can works well for memory freeing to some extent.)

Thanks,
-Kame

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