slab reassignment

Adds a "slabs reassign src dst" manual command, and a thread to safely process
slab moves in the background.

- slab freelist is now a linked list, reusing the item structure
- is -o slab_reassign is enabled, an extra background thread is started
- thread attempts to safely free up items when it's been told to move a page
  from one slab to another.

-o slab_automove is stubbed.

There are some limitations. Most notable is that you cannot repeatedly move
pages around without first having items use up the memory. Slabs with newly
assigned memory work off of a pointer, handing out chunks individually. We
would need to change that to quickly split chunks for all newly assigned pages
into that slabs freelist.

Further testing is required to ensure such is possible without impacting
performance.

1 files changed, 2 insertions, 0 deletions

diff --git a/globals.c b/globals.c
index 7d7b2a3..a01e370 100644
--- a/globals.c
+++ b/globals.c
@@ -21,3 +21,5 @@ volatile rel_time_t current_time;
 /** exported globals **/
 struct stats stats;
 struct settings settings;
+struct slab_rebalance slab_rebal;
+volatile int slab_rebalance_signal;