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

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Date:	Thu, 4 Aug 2016 14:06:07 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Aruna Ramakrishna <aruna.ramakrishna@...cle.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Mike Kravetz <mike.kravetz@...cle.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2] mm/slab: Improve performance of gathering slabinfo
 stats

On Thu,  4 Aug 2016 12:01:13 -0700 Aruna Ramakrishna <aruna.ramakrishna@...cle.com> 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.