Re: [PATCH 4/6] mm, kswapd: wake up kcompactd when kswapd had too many failures

[Mel Gorman <mgorman@techsingularity.net>]

On Thu, Jul 27, 2017 at 06:06:59PM +0200, Vlastimil Babka wrote:
> This patch deals with a corner case found when testing kcompactd with a very
> simple testcase that first fragments memory (by creating a large shmem file and
> then punching hole in every even page) and then uses artificial order-9
> GFP_NOWAIT allocations in a loop. This is freshly after virtme-run boot in KVM
> and no other activity.
> 
> What happens is that after few kswapd runs, there are no more reclaimable
> pages, and high-order pages can only be created by compaction. Because kswapd
> can't reclaim anything, pgdat->kswapd_failures increases up to
> MAX_RECLAIM_RETRIES and kswapd is no longer woken up. Thus kcompactd is also
> not woken up. After this patch, we will try to wake up kcompactd immediately
> instead of kswapd.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

If kswapd cannot make any progress then it's possible that kcompact
won'y be able to move the pages either. However, an exception is
anonymous pages without swap configured so

Acked-by: Mel Gorman <mgorman@techsingularity.net>

-- 
Mel Gorman
SUSE Labs

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