Re: [PATCH -mm 8/8] slab: reap dead memcg caches aggressively

[Christoph Lameter <cl@gentwo.org>]

On Sat, 31 May 2014, Vladimir Davydov wrote:

> > You can use a similar approach than in SLUB. Reduce the size of the per
> > cpu array objects to zero. Then SLAB will always fall back to its slow
> > path in cache_flusharray() where you may be able to do something with less
> > of an impact on performace.
>
> In contrast to SLUB, for SLAB this will slow down kfree significantly.

But that is only when you want to destroy a cache. This is similar.

> Fast path for SLAB is just putting an object to a per cpu array, while
> the slow path requires taking a per node lock, which is much slower even
> with no contention. There still can be lots of objects in a dead memcg
> cache (e.g. hundreds of megabytes of dcache), so such performance
> degradation is not acceptable, IMO.

I am not sure that there is such a stark difference to SLUB. SLUB also
takes the per node lock if necessary to handle freeing especially if you
zap the per cpu partial slab pages.