Linux 3.1 compat, shrink_*cache_memory

As of Linux 3.1 the shrink_dcache_memory and shrink_icache_memory
functions have been removed.  This same task is now accomplished
more cleanly with per super block shrinkers.  This unfortunately
leaves us no easy way to support the dnlc_reduce_cache() function.

This support has always been entirely optional.  So when no
reasonable interface is available allow the dnlc_reduce_cache()
function to effectively become a no-op.

The downside of this change is that it will prevent the zfs arc
meta data limts from being enforced.  However, the current zfs
implementation in this regard is already flawed and needs to
be reworked.  If the arc needs to enfore a meta data limit it
will need to be extended to coordinate directly with the zpl.
This will allow us to drop all this compatibility code and get
more fine grained control over the cache management.

Signed-off-by: Brian Behlendorf <[email protected]>
Issue #52

1 files changed, 4 insertions, 10 deletions

diff --git a/module/spl/spl-kmem.c b/module/spl/spl-kmem.c
index b3c054a95..1d2fa9053 100644
--- a/module/spl/spl-kmem.c
+++ b/module/spl/spl-kmem.c
@@ -2123,21 +2123,15 @@ spl_kmem_init_kallsyms_lookup(void)
 #endif /* HAVE_INVALIDATE_INODES */
 
 #ifndef HAVE_SHRINK_DCACHE_MEMORY
+	/* When shrink_dcache_memory_fn == NULL support is disabled */
 	shrink_dcache_memory_fn = (shrink_dcache_memory_t)
-	spl_kallsyms_lookup_name("shrink_dcache_memory");
-	if (!shrink_dcache_memory_fn) {
-		printk(KERN_ERR "Error: Unknown symbol shrink_dcache_memory\n");
-		return -EFAULT;
-	}
+		spl_kallsyms_lookup_name("shrink_dcache_memory");
 #endif /* HAVE_SHRINK_DCACHE_MEMORY */
 
 #ifndef HAVE_SHRINK_ICACHE_MEMORY
+	/* When shrink_icache_memory_fn == NULL support is disabled */
 	shrink_icache_memory_fn = (shrink_icache_memory_t)
-	spl_kallsyms_lookup_name("shrink_icache_memory");
-	if (!shrink_icache_memory_fn) {
-		printk(KERN_ERR "Error: Unknown symbol shrink_icache_memory\n");
-		return -EFAULT;
-	}
+		spl_kallsyms_lookup_name("shrink_icache_memory");
 #endif /* HAVE_SHRINK_ICACHE_MEMORY */
 
 	return 0;