Re: [PATCH] mm: don't wake kswapd prematurely when watermark boosting is disabled

[Mel Gorman <mgorman@suse.de>]

On Tue, Oct 20, 2020 at 01:58:33PM -0400, Johannes Weiner wrote:
> On 2-node NUMA hosts we see bursts of kswapd reclaim and subsequent
> pressure spikes and stalls from cache refaults while there is plenty
> of free memory in the system.
> 
> Usually, kswapd is woken up when all eligible nodes in an allocation
> are full. But the code related to watermark boosting can wake kswapd
> on one full node while the other one is mostly empty. This may be
> justified to fight fragmentation, but is currently unconditionally
> done whether watermark boosting is occurring or not.
> 
> In our case, many of our workloads' throughput scales with available
> memory, and pure utilization is a more tangible concern than trends
> around longer-term fragmentation. As a result we generally disable
> watermark boosting.
> 
> Wake kswapd only woken when watermark boosting is requested.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

This makes sense to the extent that I would support adding

Fixes: 1c30844d2dfe ("mm: reclaim small amounts of memory when an external fragmentation event occurs")

With or without that;

Acked-by: Mel Gorman <mgorman@suse.de>

-- 
Mel Gorman
SUSE Labs