Re: [PATCH 5/7] mm: page_alloc: Make zone distribution page agingpolicy configurable

[Rik van Riel]

On 12/13/2013 09:10 AM, Mel Gorman wrote:
> Commit 81c0a2bb ("mm: page_alloc: fair zone allocator policy") solved a
> bug whereby new pages could be reclaimed before old pages because of
> how the page allocator and kswapd interacted on the per-zone LRU lists.
> Unfortunately it was missed during review that a consequence is that
> we also round-robin between NUMA nodes. This is bad for two reasons
> 
> 1. It alters the semantics of MPOL_LOCAL without telling anyone
> 2. It incurs an immediate remote memory performance hit in exchange
>    for a potential performance gain when memory needs to be reclaimed
>    later
> 
> No cookies for the reviewers on this one.
> 
> This patch makes the behaviour of the fair zone allocator policy
> configurable.  By default it will only distribute pages that are going
> to exist on the LRU between zones local to the allocating process. This
> preserves the historical semantics of MPOL_LOCAL.
> 
> By default, slab pages are not distributed between zones after this patch is
> applied. It can be argued that they should get similar treatment but they
> have different lifecycles to LRU pages, the shrinkers are not zone-aware
> and the interaction between the page allocator and kswapd is different
> for slabs. If it turns out to be an almost universal win, we can change
> the default.
> 
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>

Acked-by: Rik van Riel <riel@xxxxxxxxxx>


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