Re: [PATCH 08/10] mm: deactivations shouldn't bias the LRU balance

[Minchan Kim]

On Mon, Jun 06, 2016 at 03:48:34PM -0400, Johannes Weiner wrote:
> Operations like MADV_FREE, FADV_DONTNEED etc. currently move any
> affected active pages to the inactive list to accelerate their reclaim
> (good) but also steer page reclaim toward that LRU type, or away from
> the other (bad).
> 
> The reason why this is undesirable is that such operations are not
> part of the regular page aging cycle, and rather a fluke that doesn't
> say much about the remaining pages on that list. They might all be in
> heavy use. But once the chunk of easy victims has been purged, the VM
> continues to apply elevated pressure on the remaining hot pages. The
> other LRU, meanwhile, might have easily reclaimable pages, and there
> was never a need to steer away from it in the first place.
> 
> As the previous patch outlined, we should focus on recording actually
> observed cost to steer the balance rather than speculating about the
> potential value of one LRU list over the other. In that spirit, leave
> explicitely deactivated pages to the LRU algorithm to pick up, and let
> rotations decide which list is the easiest to reclaim.
> 
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Nice description. Agreed.

Acked-by: Minchan Kim <minchan@xxxxxxxxxx>