slab mover rescues valid items with free chunks

During a slab page move items are typically ejected regardless of their
validity. Now, if an item is valid and free chunks are available in the same
slab class, copy the item over and replace it.

It's up to external systems to try to ensure free chunks are available before
moving a slab page. If there is no memory it will simply evict them as normal.

Also adds counters so we can finally tell how often these cases happen.

1 files changed, 2 insertions, 0 deletions

diff --git a/items.h b/items.h
index b091fa0..f47de8f 100644
--- a/items.h
+++ b/items.h
@@ -14,6 +14,8 @@ void do_item_update(item *it);   /** update LRU time to current and reposition *
 void do_item_update_nolock(item *it);
 int  do_item_replace(item *it, item *new_it, const uint32_t hv);
 
+int item_is_flushed(item *it);
+
 /*@null@*/
 char *item_cachedump(const unsigned int slabs_clsid, const unsigned int limit, unsigned int *bytes);
 void item_stats(ADD_STAT add_stats, void *c);