Remove skc_ref from alloc/free paths

As described in spl_kmem_cache_destroy() the ->skc_ref count was
added to address the case of a cache reap or grow racing with a
destroy.  They are not strictly needed in the alloc/free paths
because consumers of the cache are responsible for not using it
while it's being destroyed.

Removing this code is desirable because there is some evidence that
contention on this atomic negative impacts performance on large-scale
NUMA systems.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tim Chase <tim@chase2k.com>
Issue #463

diff --git a/module/spl/spl-kmem-cache.c b/module/spl/spl-kmem-cache.c
index 112d0f8768aa254036f382e06a8729bf52cce7b1..0417f9d0b826aea34eeedf94a600321c99d2df18 100644 (file)
--- a/module/spl/spl-kmem-cache.c
+++ b/module/spl/spl-kmem-cache.c
@@ -1403,8 +1403,6 @@ spl_kmem_cache_alloc(spl_kmem_cache_t *skc, int flags)
        ASSERT(skc->skc_magic == SKC_MAGIC);
        ASSERT(!test_bit(KMC_BIT_DESTROY, &skc->skc_flags));
 
-       atomic_inc(&skc->skc_ref);
-
        /*
         * Allocate directly from a Linux slab.  All optimizations are left
         * to the underlying cache we only need to guarantee that KM_SLEEP
@@ -1457,8 +1455,6 @@ ret:
                        prefetchw(obj);
        }
 
-       atomic_dec(&skc->skc_ref);
-
        return (obj);
 }
 EXPORT_SYMBOL(spl_kmem_cache_alloc);
@@ -1479,7 +1475,6 @@ spl_kmem_cache_free(spl_kmem_cache_t *skc, void *obj)
 
        ASSERT(skc->skc_magic == SKC_MAGIC);
        ASSERT(!test_bit(KMC_BIT_DESTROY, &skc->skc_flags));
-       atomic_inc(&skc->skc_ref);
 
        /*
         * Run the destructor
@@ -1492,7 +1487,7 @@ spl_kmem_cache_free(spl_kmem_cache_t *skc, void *obj)
         */
        if (skc->skc_flags & KMC_SLAB) {
                kmem_cache_free(skc->skc_linux_cache, obj);
-               goto out;
+               return;
        }
 
        /*
@@ -1507,7 +1502,7 @@ spl_kmem_cache_free(spl_kmem_cache_t *skc, void *obj)
                spin_unlock(&skc->skc_lock);
 
                if (do_emergency && (spl_emergency_free(skc, obj) == 0))
-                       goto out;
+                       return;
        }
 
        local_irq_save(flags);
@@ -1538,8 +1533,6 @@ spl_kmem_cache_free(spl_kmem_cache_t *skc, void *obj)
 
        if (do_reclaim)
                spl_slab_reclaim(skc);
-out:
-       atomic_dec(&skc->skc_ref);
 }
 EXPORT_SYMBOL(spl_kmem_cache_free);