On 08/29/2016 05:44 PM, Aruna Ramakrishna 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.

Signed-off-by: Aruna Ramakrishna <redacted>
Cc: Mike Kravetz <redacted>
Cc: Christoph Lameter <redacted>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <redacted>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
Note: this has been tested only on x86_64.

This patch has spawned off a very interesting discussion in a older 
thread, and I guess the latest incarnation of this patch got buried. I'm 
resending it for review/approval.

Thanks,
Aruna

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