Re: [PATCH v2 04/29] slub: always get the cache from its page inkfree

[Glauber Costa]

On 05/11/2012 04:20 PM, Christoph Lameter wrote:
> On Fri, 11 May 2012, Glauber Costa wrote:
>
> > > I see that. But there are other subsystems from slab allocators that do
> > > the same. There are also objects that may be used by multiple processes.
> >
> > This is also true for normal user pages. And then, we do what memcg does:
> > first one to touch, gets accounted. I don't think deviating from the memcg
> > behavior for user pages makes much sense here.
> >
> > A cache won't go away while it still have objects, even after the memcg is
> > removed (it is marked as dead)
>
> Ok so we will have some dead pages around that are then repatriated to
> the / set?

No, they are not repatriated. I actually wrote code for that once in my 
first series, but it was the general feeling at the time that it was too 
complicated. (and I only tried for the slub, not slab)

So instead, we just keep the cache around, until the objects go away.
It will show in slabinfo as dentry(css_id:memcgname)dead

For the record, I wrote that code because I found a nice feature, but I 
totally agree with the complicated part.

Also, in normal scenarios, dead caches are not expected to be common. 
Most of them should go away as memcg dies.

> > > Hmmm.. Would be better to have a hierachy there. /proc/slabinfo is more
> > > legacy.
> >
> > I can take a look at that then. Assuming you agree with all the rest, is
> > looking into that a pre-requisite for merging, or is something that can be
> > deferred for a phase2 ? (We still don't do shrinkers, for instance, so this is
> > sure to have a phase2)
>
> Not a prerequisite for merging but note that I intend to rework the
> allocators to extract common code so that they have the same sysfs
> interface, error reporting and failure scenarios. We can at that time
> also add support for /sys/kernel/slab to memcg. (/sys/memcg/<name>/slab/* ?)

Yes, that would be a good plan.


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