Re: [PATCH v2] mm/slab: Improve performance of gathering slabinfo stats

[Aruna Ramakrishna]

On 08/04/2016 02:06 PM, Andrew Morton wrote:
> On Thu,  4 Aug 2016 12:01:13 -0700 Aruna Ramakrishna <aruna.ramakrishna@xxxxxxxxxx> wrote:
>
> > On large systems, when some slab caches grow to millions of objects (and
> > many gigabytes), running 'cat /proc/slabinfo' can take up to 1-2 seconds.
> > During this time, interrupts are disabled while walking the slab lists
> > (slabs_full, slabs_partial, and slabs_free) for each node, and this
> > sometimes causes timeouts in other drivers (for instance, Infiniband).
> >
> > This patch optimizes 'cat /proc/slabinfo' by maintaining a counter for
> > total number of allocated slabs per node, per cache. This counter is
> > updated when a slab is created or destroyed. This enables us to skip
> > traversing the slabs_full list while gathering slabinfo statistics, and
> > since slabs_full tends to be the biggest list when the cache is large, it
> > results in a dramatic performance improvement. Getting slabinfo statistics
> > now only requires walking the slabs_free and slabs_partial lists, and
> > those lists are usually much smaller than slabs_full. We tested this after
> > growing the dentry cache to 70GB, and the performance improved from 2s to
> > 5ms.
>
> I assume this is tested on both slab and slub?
>
> It isn't the smallest of patches but given the seriousness of the
> problem I think I'll tag it for -stable backporting.

This was only sanity-checked on slub. The performance tests were only 
run on slab.

Thanks,
Aruna