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

[Andrew Morton]

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.