Add spl_kmem_cache_reclaim module option

The correct behavior for all registered shrinkers is to return the
number of objects in their cache.  In theory this allows the Linux
VM to balance memory reclaim across all registered caches.

In commit b9b3715 this behavior was disabled in favor of returning
-1 which notifies the VM that no additional objects are available
for reclaim.  This was done as a workaround to resolve thrashing
in shrink_slabs() which could occur when memory was low and numerous
core where in reclaim.  Unfortunately, this has been observed to
increase the likelihood of OOM events when SPL slab consumers are
responsible for consuming the majority of memory.

Therefore, this patch makes this behavior tunable.  Setting the
spl_kmem_cache_reclaim module option to 0x1 will result in the
shrinker only being called once.  This is the default behavior.

Signed-off-by: Brian Behlendorf <[email protected]>
Signed-off-by: Prakash Surya <[email protected]>
Closes #358

1 files changed, 2 insertions, 0 deletions

diff --git a/include/sys/kmem.h b/include/sys/kmem.h
index 18533fe39..3418d3dd4 100644
--- a/include/sys/kmem.h
+++ b/include/sys/kmem.h
@@ -385,6 +385,8 @@ typedef enum kmem_cbrc {
 #define KMC_EXPIRE_AGE		0x1     /* Due to age */
 #define KMC_EXPIRE_MEM		0x2     /* Due to low memory */
 
+#define	KMC_RECLAIM_ONCE	0x1	/* Force a single shrinker pass */
+
 extern unsigned int spl_kmem_cache_expire;
 extern struct list_head spl_kmem_cache_list;
 extern struct rw_semaphore spl_kmem_cache_sem;