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
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