Re: [PATCH 3/9] mm: zone_reclaim: compaction: don't depend on kswapd to invoke reset_isolation_suitable

[Johannes Weiner <hannes@cmpxchg.org>]

On Fri, Aug 02, 2013 at 06:06:30PM +0200, Andrea Arcangeli wrote:
> If kswapd never need to run (only __GFP_NO_KSWAPD allocations and
> plenty of free memory) compaction is otherwise crippled down and stops
> running for a while after the free/isolation cursor meets. After that
> allocation can fail for a full cycle of compaction_deferred, until
> compaction_restarting finally reset it again.
> 
> Stopping compaction for a full cycle after the cursor meets, even if
> it never failed and it's not going to fail, doesn't make sense.
> 
> We already throttle compaction CPU utilization using
> defer_compaction. We shouldn't prevent compaction to run after each
> pass completes when the cursor meets, unless it failed.
> 
> This makes direct compaction functional again. The throttling of
> direct compaction is still controlled by the defer_compaction
> logic.
> 
> kswapd still won't risk to reset compaction, and it will wait direct
> compaction to do so. Not sure if this is ideal but it at least
> decreases the risk of kswapd doing too much work. kswapd will only run
> one pass of compaction until some allocation invokes compaction again.
> 
> This decreased reliability of compaction was introduced in commit
> 62997027ca5b3d4618198ed8b1aba40b61b1137b .
> 
> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
> Reviewed-by: Rik van Riel <riel@redhat.com>
> Acked-by: Rafael Aquini <aquini@redhat.com>
> Acked-by: Mel Gorman <mgorman@suse.de>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

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