Add an estimate of per-allocation overhead.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/include/btree.i b/src/include/btree.i
index 52769d837dc..8826a88ba0d 100644
--- a/src/include/btree.i
+++ b/src/include/btree.i
@@ -41,6 +41,14 @@ __wt_eviction_page_force(WT_SESSION_IMPL *session, WT_PAGE *page)
 }
 
 /*
+ * Estimate the per-allocation overhead.  All allocators have some kind of
+ * header and pad for alignment.  We can't know for sure what that adds up
+ * to, but this is an estimate based on some measurements of heap size versus
+ * bytes in use.
+ */
+#define	WT_ALLOC_OVERHEAD      32
+
+/*
  * __wt_cache_page_inmem_incr --
  *	Increment a page's memory footprint in the cache.
  */
@@ -49,6 +57,8 @@ __wt_cache_page_inmem_incr(WT_SESSION_IMPL *session, WT_PAGE *page, size_t size)
 {
 	WT_CACHE *cache;
 
+	size += WT_ALLOC_OVERHEAD;
+
 	cache = S2C(session)->cache;
 	(void)WT_ATOMIC_ADD(cache->bytes_inmem, size);
 	(void)WT_ATOMIC_ADD(page->memory_footprint, WT_STORE_SIZE(size));
@@ -65,6 +75,8 @@ __wt_cache_page_inmem_decr(WT_SESSION_IMPL *session, WT_PAGE *page, size_t size)
 {
 	WT_CACHE *cache;
 
+	size += WT_ALLOC_OVERHEAD;
+
 	cache = S2C(session)->cache;
 	(void)WT_ATOMIC_SUB(cache->bytes_inmem, size);
 	(void)WT_ATOMIC_SUB(page->memory_footprint, WT_STORE_SIZE(size));