Merge pull request #2351 from wiredtiger/wt-2253-readgen-oldest-eviction

WT-2553: prioritize WT_READGEN_OLDEST pages for eviction.

src/evict/evict_lru.c

@@ -36,6 +36,10 @@ __evict_read_gen(const WT_EVICT_ENTRY *entry)
 
 	page = entry->ref->page;
 
+	/* Any page set to the oldest generation should be discarded. */
+	if (page->read_gen == WT_READGEN_OLDEST)
+		return (WT_READGEN_OLDEST);
+
 	/* Any empty page (leaf or internal), is a good choice. */
 	if (__wt_page_is_empty(page))
 		return (WT_READGEN_OLDEST);