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Re: [PATCH v3 15/16] memcg/sl[au]b: shrink dead caches [message #48014 is a reply to message #48002] Mon, 24 September 2012 17:43 Go to previous messageGo to previous message
Tejun Heo is currently offline  Tejun Heo
Messages: 184
Registered: November 2006
Senior Member
Hello,

On Mon, Sep 24, 2012 at 12:25:00PM +0400, Glauber Costa wrote:
> > This is kinda nasty. Do we really need to do this? How long would a
> > dead cache stick around?
>
> Without targeted shrinking, until all objects are manually freed, which
> may need to wait global reclaim to kick in.
>
> In general, if we agree with duplicating the caches, the problem that
> they may stick around for some time will not be avoidable. If you have
> any suggestions about alternative ways for it, I'm all ears.

I don't have much problem with caches sticking around waiting to be
reaped. I'm just wondering whether renaming trick is really
necessary.

> > Reaping dead caches doesn't exactly sound like a high priority thing
> > and adding a branch to hot path for that might not be the best way to
> > do it. Why not schedule an extremely lazy deferrable delayed_work
> > which polls for emptiness, say, every miniute or whatever?
> >
>
> Because this branch is marked as unlikely, I would expect it not to be a
> big problem. It will be not taken most of the time, and becomes a very
> cheap branch. I considered this to be simpler than a deferred work
> mechanism.
>
> If even then, you guys believe this is still too high, I can resort to that.

It's still an otherwise unnecessary branch on a very hot path. If you
can remove it, there's no reason not to.

Thanks.

--
tejun
 
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