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
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