extstore: make defaults more aggressive

extstore has a background thread which examines slab classes for items
to flush to disk. The thresholds for flushing to disk are managed by a
specialized "slab automove" algorithm. This algorithm was written in
2017 and not tuned since.

Most serious users set "ext_item_age=0" and force flush all items. This
is partially because the defaults do not flush aggressively enough,
which causes memory to run out and evictions to happen.

This change simplifies the slab automove portion. Instead of balancing
free chunks of memory per slab class, it sets a target of a certain
number of free global pages.

The extstore flusher thread also uses the page pool and some low chunk
limits to decide when to start flushing. Its sleep routines have also
been adjusted as it could oversleep too easily.

A few other small changes were required to avoid over-moving slab pages
around.

1 files changed, 1 insertions, 7 deletions

diff --git a/items.c b/items.c
index e5347cc..9cee07e 100644
--- a/items.c
+++ b/items.c
@@ -1669,13 +1669,7 @@ static void *lru_maintainer_thread(void *arg) {
                 LOGGER_LOG(l, LOG_SYSEVENTS, LOGGER_SLAB_MOVE, NULL,
                         src, dst);
             }
-            // dst == 0 means reclaim to global pool, be more aggressive
-            if (dst != 0) {
-                last_automove_check = current_time;
-            } else if (dst == 0) {
-                // also ensure we minimize the thread sleep
-                to_sleep = 1000;
-            }
+            last_automove_check = current_time;
         }
     }
     pthread_mutex_unlock(&lru_maintainer_lock);