WT-2910 When running in-memory, only evict dirty pages. (#3044)

* Don't relax the clean / dirty requirements when we get aggressive: if application threads are blocked by the dirty limit, evicting a clean page doesn't unblock them so there's no point trying.

* Sanity check dirty eviction limits: once the cache is full, we should evict both clean and dirty pages.

2 files changed, 42 insertions, 5 deletions

diff --git a/src/conn/conn_cache.c b/src/conn/conn_cache.c
index 7e94e9e87dc..6788b1f7f47 100644
--- a/src/conn/conn_cache.c
+++ b/src/conn/conn_cache.c
@@ -56,6 +56,13 @@ __cache_config_local(WT_SESSION_IMPL *session, bool shared, const char *cfg[])
 		cache->eviction_dirty_target = (u_int)cval.val;
 
 		/*
+		 * Don't allow the dirty target to be larger than the overall
+		 * target.
+		 */
+		if (cache->eviction_dirty_target > cache->eviction_target)
+			cache->eviction_dirty_target = cache->eviction_target;
+
+		/*
 		 * Sanity check the checkpoint target: don't allow a value
 		 * lower than the dirty target.
 		 */
@@ -68,6 +75,13 @@ __cache_config_local(WT_SESSION_IMPL *session, bool shared, const char *cfg[])
 		WT_RET(__wt_config_gets(
 		    session, cfg, "eviction_dirty_trigger", &cval));
 		cache->eviction_dirty_trigger = (u_int)cval.val;
+
+		/*
+		 * Don't allow the dirty trigger to be larger than the overall
+		 * trigger or we can get stuck with a cache full of dirty data.
+		 */
+		if (cache->eviction_dirty_trigger > cache->eviction_trigger)
+			cache->eviction_dirty_trigger = cache->eviction_trigger;
 	}
 
 	WT_RET(__wt_config_gets(session, cfg, "eviction.threads_max", &cval));
diff --git a/src/evict/evict_lru.c b/src/evict/evict_lru.c
index cc4d8ea1e08..843249b695d 100644
--- a/src/evict/evict_lru.c
+++ b/src/evict/evict_lru.c
@@ -468,6 +468,14 @@ __evict_update_work(WT_SESSION_IMPL *session)
 		F_SET(cache, WT_CACHE_EVICT_DIRTY_HARD);
 
 	/*
+	 * If application threads are blocked by the total volume of data in
+	 * cache, try dirty pages as well.
+	 */
+	if (__wt_cache_aggressive(session) &&
+	    F_ISSET(cache, WT_CACHE_EVICT_CLEAN_HARD))
+		F_SET(cache, WT_CACHE_EVICT_DIRTY);
+
+	/*
 	 * Scrub dirty pages and keep them in cache if we are less than half
 	 * way to the clean or dirty trigger.
 	 */
@@ -477,6 +485,18 @@ __evict_update_work(WT_SESSION_IMPL *session)
 	    bytes_max) / 200)
 		F_SET(cache, WT_CACHE_EVICT_SCRUB);
 
+	/*
+	 * With an in-memory cache, we only do dirty eviction in order to scrub
+	 * pages.
+	 */
+	if (F_ISSET(conn, WT_CONN_IN_MEMORY)) {
+		if (F_ISSET(cache, WT_CACHE_EVICT_CLEAN))
+			F_SET(cache, WT_CACHE_EVICT_DIRTY);
+		if (F_ISSET(cache, WT_CACHE_EVICT_CLEAN_HARD))
+			F_SET(cache, WT_CACHE_EVICT_DIRTY_HARD);
+		F_CLR(cache, WT_CACHE_EVICT_CLEAN | WT_CACHE_EVICT_CLEAN_HARD);
+	}
+
 	WT_STAT_CONN_SET(session, cache_eviction_state,
 	    F_MASK(cache, WT_CACHE_EVICT_MASK));
 
@@ -1348,7 +1368,7 @@ __evict_walk_file(WT_SESSION_IMPL *session,
 	    ret = __wt_tree_walk_count(
 	    session, &btree->evict_ref, &refs_walked, walk_flags)) {
 		/*
-		 * Check whether we're finding a good ration of candidates vs
+		 * Check whether we're finding a good ratio of candidates vs
 		 * pages seen.  Some workloads create "deserts" in trees where
 		 * no good eviction candidates can be found.  Abandon the walk
 		 * if we get into that situation.
@@ -1402,20 +1422,23 @@ __evict_walk_file(WT_SESSION_IMPL *session,
 			continue;
 		}
 
+		/* Pages that are empty or from dead trees are also good. */
 		if (__wt_page_is_empty(page) ||
-		    F_ISSET(session->dhandle, WT_DHANDLE_DEAD) ||
-		    __wt_cache_aggressive(session))
+		    F_ISSET(session->dhandle, WT_DHANDLE_DEAD))
 			goto fast;
 
 		/* Skip clean pages if appropriate. */
-		if (!modified && (F_ISSET(conn, WT_CONN_IN_MEMORY) ||
-		    !F_ISSET(cache, WT_CACHE_EVICT_CLEAN)))
+		if (!modified && !F_ISSET(cache, WT_CACHE_EVICT_CLEAN))
 			continue;
 
 		/* Skip dirty pages if appropriate. */
 		if (modified && !F_ISSET(cache, WT_CACHE_EVICT_DIRTY))
 			continue;
 
+		/* If eviction gets aggressive, anything else is fair game. */
+		if (__wt_cache_aggressive(session))
+			goto fast;
+
 		/* Limit internal pages to 50% of the total. */
 		if (WT_PAGE_IS_INTERNAL(page) &&
 		    internal_pages >= (int)(evict - start) / 2)