The vmem callback to reclaim kmem arena address space on low or

fragmented conditions currently just wakes up the pagedaemon.  The
kmem arena is significantly smaller then the total available physical
memory, which means that there are loads where kmem arena space could
be exhausted, while there is a lot of pages available still.  The
woken up pagedaemon sees vm_pages_needed != 0, verifies the condition
vm_paging_needed() which is false, clears the pass and returns back to
sleep, not calling neither uma_reclaim() nor lowmem handler.

To handle low kmem arena conditions, create additional pagedaemon
thread which calls uma_reclaim() directly.  The thread sleeps on the
dedicated channel and kmem_reclaim() wakes the thread in addition to
the pagedaemon.

Reported and tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks

1 files changed, 3 insertions, 0 deletions

diff --git a/sys/vm/uma.h b/sys/vm/uma.h
index df6cc5c7a118..d3e0658aef15 100644
--- a/sys/vm/uma.h
+++ b/sys/vm/uma.h
@@ -690,4 +690,7 @@ struct uma_percpu_stat {
 	uint64_t	_ups_reserved[5];	/* Reserved. */
 };
 
+void uma_reclaim_wakeup(void);
+void uma_reclaim_worker(void *);
+
 #endif	/* _VM_UMA_H_ */