libglusterfs: provide standardized atomic operations

The current macros ATOMIC_INCREMENT() and ATOMIC_DECREMENT() expect a
lock as first argument. There are at least two issues with this
approach:

  1. this lock is unused on architectures that have atomic operations
  2. some structures use a single lock for multiple variables

By defining a gf_atomic_t type, the unused lock can be removed, saving a
few bytes on modern architectures.

Because the gf_atomic_t type locates the lock for the variable (in case
of older architectures), each variable is protected the same on all
architectures. This makes the behaviour across all architectures more
equal (per variable locking, by a gf_lock_t or compiler optimization).

BUG: 1437037
Change-Id: Ic164892b06ea676e6a9566f8a98b7faf0efe76d6
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: https://review.gluster.org/16963
Smoke: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Xavier Hernandez <xhernandez@datalab.es>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Reviewed-by: Jeff Darcy <jeff@pl.atyp.us>

1 files changed, 2 insertions, 8 deletions

diff --git a/libglusterfs/src/mem-pool.h b/libglusterfs/src/mem-pool.h
index 0dc186341b2..1b27119cf6c 100644
--- a/libglusterfs/src/mem-pool.h
+++ b/libglusterfs/src/mem-pool.h
@@ -13,6 +13,7 @@
 
 #include "list.h"
 #include "locking.h"
+#include "atomic.h"
 #include "logging.h"
 #include "mem-types.h"
 #include <stdlib.h>
@@ -48,14 +49,7 @@ struct mem_acct_rec {
 
 struct mem_acct {
         uint32_t            num_types;
-        /*
-         * The lock is only used on ancient platforms (e.g. RHEL5) to keep
-         * refcnt increment/decrement atomic.  We could even make its existence
-         * conditional on the right set of version/feature checks, but it's so
-         * lightweight that it's not worth the obfuscation.
-         */
-        gf_lock_t           lock;
-        unsigned int        refcnt;
+        gf_atomic_t         refcnt;
         struct mem_acct_rec rec[0];
 };