core: fix memory allocation issues

Two problems have been identified that caused that gluster's memory
usage were twice higher than required.

1. An off by 1 error caused that all objects allocated from the memory
   pools were taken from a pool bigger than required. Since each pool
   corresponds to a size equal to a power of two, this was wasting half
   of the available memory.

2. The header information used for accounting on each memory object was
   not taken into consideration when searching for a suitable memory
   pool. It was added later when each individual block was allocated.
   This made this space "invisible" to memory accounting.

Credits: Thanks to Nithya Balachandran for identifying this problem and
         testing this patch.

Backport of:
> BUG: 1722802
> Change-Id: I90e27ad795fe51ca11c13080f62207451f6c138c
> Signed-off-by: Xavi Hernandez <xhernandez@redhat.com>

Fixes: bz#1724210
Change-Id: I90e27ad795fe51ca11c13080f62207451f6c138c
Signed-off-by: Xavi Hernandez <xhernandez@redhat.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/libglusterfs/src/glusterfs/mem-pool.h b/libglusterfs/src/glusterfs/mem-pool.h
index c5a486b4cc8..be0a26d3f64 100644
--- a/libglusterfs/src/glusterfs/mem-pool.h
+++ b/libglusterfs/src/glusterfs/mem-pool.h
@@ -231,7 +231,10 @@ typedef struct pooled_obj_hdr {
     struct mem_pool *pool;
 } pooled_obj_hdr_t;
 
-#define AVAILABLE_SIZE(p2) (1 << (p2))
+/* Each memory block inside a pool has a fixed size that is a power of two.
+ * However each object will have a header that will reduce the available
+ * space. */
+#define AVAILABLE_SIZE(p2) ((1UL << (p2)) - sizeof(pooled_obj_hdr_t))
 
 typedef struct per_thread_pool {
     /* the pool that was used to request this allocation */