Re: [PATCH] cache align vm_stat

From: Mel Gorman
Date: Thu Oct 27 2011 - 04:50:39 EST

On Mon, Oct 24, 2011 at 11:10:35AM -0500, Dimitri Sivanich wrote:
> Avoid false sharing of the vm_stat array.
> This was found to adversely affect tmpfs I/O performance.

I think this fix is overly simplistic. It is moving each counter into
its own cache line. While I accept that this will help the preformance
of the tmpfs-based workload, it will adversely affect workloads that
touch a lot of counters because of the increased cache footprint.

1. Is it possible to rearrange the vmstat array such that two hot
counters do not share a cache line?
2. Has Andrew's suggestion to alter the per-cpu threshold based on the
value of the global counter to reduce conflicts been tried?

(I'm at Linux Con at the moment so will be even slower to respond than

Mel Gorman
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