Re: memo: mem+swap controller

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

On Fri, 01 Aug 2008 09:43:43 +0530, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> Daisuke Nishimura wrote:
> > On Fri, 01 Aug 2008 08:58:07 +0530, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> >> Daisuke Nishimura wrote:
> >>> Hi, Kamezawa-san.
> >>>
> >>> On Thu, 31 Jul 2008 10:15:33 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> >>>> Hi, mem+swap controller is suggested by Hugh Dickins and I think it's a great
> >>>> idea. Its concept is having 2 limits. (please point out if I misunderstand.)
> >>>>
> >>>>  - memory.limit_in_bytes       .... limit memory usage.
> >>>>  - memory.total_limit_in_bytes .... limit memory+swap usage.
> >>>>
> >>> When I've considered more, I wonder how we can accomplish
> >>> "do not use swap in this group".
> >>>
> >> It's easy use the memrlimit controller and set virtual address limit <=
> >> memory.limit_in_bytes. I use that to make sure I never swap out.
> >>
> > I don't think it works under memory pressure *outside* of the group,
> > that is, global memory reclaim.
> > (I think "limit_in_bytes == total_limit_in_bytes" also works *inside* memory 
> > pressure.)
> > 
> 
> Yes, but it ensures that the current cgroup does not add to global swap
> pressure. Trying to control global pressure from inside a cgroup might be hard,
> but I see your intention of isolating the cgroup from global pressure. With
> swappiness, it should be possible to purge page cache ahead of creating swap
> pressure.
> 
Ah, I don't have strong requirement of "do not use swap in this group"
under global memory pressure(and it would be bad policy).
I asked just for curiosity. Sorry for confusing you.

> >>> Setting "limit_in_bytes == total_limit_in_bytes" doesn't meet it, I think.
> >>> "limit_in_bytes = total_limit_in_bytes = 1G" cannot
> >>> avoid "memory.usage = 700M swap.usage = 300M" under memory pressure
> >>> outside of the group(and I think this behavior is the diffrence
> >>> of "memory controller + swap controller" and "mem+swap controller").
> >>>
> >>> I think total_limit_in_bytes and swappiness(or some flag to indicate
> >>> "do not swap out"?) for each group would make more sense.
> >> I do intend to add the swappiness feature soon for control groups.
> >>
> > How does it work?
> > Does it affect global page reclaim?
> > 
> 
> We have a swappiness parameter in scan_control. Each control group indicates
> what it wants it swappiness to be when the control group is over it's limit and
> reclaim kicks in.
> 
I see. Thank you for your explanation.


Thanks,
Daisuke Nishimura.

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