Re: [PATCH] mm: fadvise: avoid expensive remote LRU cache draining after FADV_DONTNEED

[Mel Gorman]

On Sat, Dec 10, 2016 at 12:26:58PM -0500, Johannes Weiner wrote:
> When FADV_DONTNEED cannot drop all pages in the range, it observes
> that some pages might still be on per-cpu LRU caches after recent
> instantiation and so initiates remote calls to all CPUs to flush their
> local caches. However, in most cases, the fadvise happens from the
> same context that instantiated the pages, and any pre-LRU pages in the
> specified range are most likely sitting on the local CPU's LRU cache,
> and so in many cases this results in unnecessary remote calls, which,
> in a loaded system, can hold up the fadvise() call significantly.
> 
> Try to avoid the remote call by flushing the local LRU cache before
> even attempting to invalidate anything. It's a cheap operation, and
> the local LRU cache is the most likely to hold any pre-LRU pages in
> the specified fadvise range.
> 
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Acked-by: Mel Gorman <mgorman@xxxxxxx>

-- 
Mel Gorman
SUSE Labs