Re: [PATCH 0/2] Disable zone_reclaim_mode by default

[Mel Gorman]

On Tue, Apr 08, 2014 at 03:56:49PM -0400, Josh Berkus wrote:
> On 04/08/2014 03:53 PM, Robert Haas wrote:
> > In an ideal world, the kernel would put the hottest pages on the local
> > node and the less-hot pages on remote nodes, moving pages around as
> > the workload shifts.  In practice, that's probably pretty hard.
> > Fortunately, it's not nearly as important as making sure we don't
> > unnecessarily hit the disk, which is infinitely slower than any memory
> > bank.
> 
> Even if the kernel could do this, we would *still* have to disable it
> for PostgreSQL, since our double-buffering makes our pages look "cold"
> to the kernel ... as discussed.
> 

If it's the shared mapping that is being used then automatic NUMA
balancing should migrate those pages to a node local to the CPU
accessing it but how well it works will partially depend on how much
those accesses move around. It's independent of the zone_reclaim_mode
issue.

-- 
Mel Gorman
SUSE Labs
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