Re: [PATCH 2/2] free_pcppages_bulk: prefetch buddy while not holding lock

[Dave Hansen]

On 01/24/2018 08:43 AM, Mel Gorman wrote:
> I'm less convinced by this for a microbenchmark. Prefetch has not been a
> universal win in the past and we cannot be sure that it's a good idea on
> all architectures or doesn't have other side-effects such as consuming
> memory bandwidth for data we don't need or evicting cache hot data for
> buddy information that is not used.

I had the same reaction.

But, I think this case is special.  We *always* do buddy merging (well,
before the next patch in the series is applied) and check an order-0
page's buddy to try to merge it when it goes into the main allocator.
So, the cacheline will always come in.

IOW, I don't think this has the same downsides normally associated with
prefetch() since the data is always used.