Expose max/min objs per slab and max slab size

By default maximal number of objects in slab can't exceed (16*2 - 1) and slab
size can't exceed 32M.
Today's high end servers having couple hundreds of RAM available for ARC may
run into a trouble with virtual memory because of the restriction mentioned
above.

Problem:
Reasons for very high number of virtual memory allocations:
	* Real slab size very small relative to the size of the entire RAM
	* Slabs allocated on virtual memory and fill entire ARC

The result is very high number of allocated virtual memory ranges (hundreds of
ranges). When virtual memory subsystem manages high number of ranges its
performance become so poor that it freezes from time to time.

Solution:
Number of objects per slab should be increased taking into account maximal
slab size which can also be increased if needed.

Signed-off-by: Andrey Vesnovaty <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #337

1 files changed, 19 insertions, 6 deletions

diff --git a/module/spl/spl-kmem.c b/module/spl/spl-kmem.c
index 23e47808a..e43e9170b 100644
--- a/module/spl/spl-kmem.c
+++ b/module/spl/spl-kmem.c
@@ -46,6 +46,19 @@ EXPORT_SYMBOL(spl_kmem_cache_expire);
 module_param(spl_kmem_cache_expire, uint, 0644);
 MODULE_PARM_DESC(spl_kmem_cache_expire, "By age (0x1) or low memory (0x2)");
 
+unsigned int spl_kmem_cache_obj_per_slab = SPL_KMEM_CACHE_OBJ_PER_SLAB;
+module_param(spl_kmem_cache_obj_per_slab, uint, 0644);
+MODULE_PARM_DESC(spl_kmem_cache_obj_per_slab, "Number of objects per slab");
+
+unsigned int spl_kmem_cache_obj_per_slab_min = SPL_KMEM_CACHE_OBJ_PER_SLAB_MIN;
+module_param(spl_kmem_cache_obj_per_slab_min, uint, 0644);
+MODULE_PARM_DESC(spl_kmem_cache_obj_per_slab_min,
+    "Minimal number of objects per slab");
+
+unsigned int spl_kmem_cache_max_size = 32;
+module_param(spl_kmem_cache_max_size, uint, 0644);
+MODULE_PARM_DESC(spl_kmem_cache_max_size, "Maximum size of slab in MB");
+
 /*
  * The minimum amount of memory measured in pages to be free at all
  * times on the system.  This is similar to Linux's zone->pages_min
@@ -1355,10 +1368,10 @@ spl_cache_age(void *data)
 
 /*
  * Size a slab based on the size of each aligned object plus spl_kmem_obj_t.
- * When on-slab we want to target SPL_KMEM_CACHE_OBJ_PER_SLAB.  However,
+ * When on-slab we want to target spl_kmem_cache_obj_per_slab.  However,
  * for very small objects we may end up with more than this so as not
  * to waste space in the minimal allocation of a single page.  Also for
- * very large objects we may use as few as SPL_KMEM_CACHE_OBJ_PER_SLAB_MIN,
+ * very large objects we may use as few as spl_kmem_cache_obj_per_slab_min,
  * lower than this and we will fail.
  */
 static int
@@ -1367,7 +1380,7 @@ spl_slab_size(spl_kmem_cache_t *skc, uint32_t *objs, uint32_t *size)
 	uint32_t sks_size, obj_size, max_size;
 
 	if (skc->skc_flags & KMC_OFFSLAB) {
-		*objs = SPL_KMEM_CACHE_OBJ_PER_SLAB;
+		*objs = spl_kmem_cache_obj_per_slab;
 		*size = P2ROUNDUP(sizeof(spl_kmem_slab_t), PAGE_SIZE);
 		SRETURN(0);
 	} else {
@@ -1377,12 +1390,12 @@ spl_slab_size(spl_kmem_cache_t *skc, uint32_t *objs, uint32_t *size)
 		if (skc->skc_flags & KMC_KMEM)
 			max_size = ((uint32_t)1 << (MAX_ORDER-3)) * PAGE_SIZE;
 		else
-			max_size = (32 * 1024 * 1024);
+			max_size = (spl_kmem_cache_max_size * 1024 * 1024);
 
 		/* Power of two sized slab */
 		for (*size = PAGE_SIZE; *size <= max_size; *size *= 2) {
 			*objs = (*size - sks_size) / obj_size;
-			if (*objs >= SPL_KMEM_CACHE_OBJ_PER_SLAB)
+			if (*objs >= spl_kmem_cache_obj_per_slab)
 				SRETURN(0);
 		}
 
@@ -1393,7 +1406,7 @@ spl_slab_size(spl_kmem_cache_t *skc, uint32_t *objs, uint32_t *size)
 		 */
 		*size = max_size;
 		*objs = (*size - sks_size) / obj_size;
-		if (*objs >= SPL_KMEM_CACHE_OBJ_PER_SLAB_MIN)
+		if (*objs >= (spl_kmem_cache_obj_per_slab_min))
 			SRETURN(0);
 	}