Re: [lkp] [mm] 795ae7a0de: pixz.throughput -9.1% regression

From: Mel Gorman
Date: Fri Jun 03 2016 - 05:01:02 EST

On Thu, Jun 02, 2016 at 12:07:06PM -0400, Johannes Weiner wrote:
> right before the test is running? I wonder if it's mostly filled with
> cache, and the increase in watermarks causes a higher portion of the
> anon allocs and frees to spill to the remote node, but never enough to
> enter the allocator slowpath and waking kswapd to fix it.
> Another suspect is the fair zone allocator, whose allocation batches
> increased as well. It shouldn't affect NUMA placement, but I wonder if
> there is a bug in there that causes false spilling to foreign nodes
> that was only bounded by the allocation batch of the foreign zone.
> Mel, does such a symptom sound familiar in any way?

Unfortunately not. The closest I've seen recently is bugs in the page
allocator patches that artifically enters the slow path prematurely but
that does not appear to apply here.

Mel Gorman