extstore: prefill global page pool with extstore

the slab page mover algo would fill memory to evicting for a few seconds
before jumping to life and shoveling some pages into the global pool.

swore I was going to fix this post-release, but I had a moment of inspiration
after finding some code from another branch that did half the work. After a
bunch of stupid bugs it seems to work.

-o slab_automove_freeratio=0.N is now an option. This is *percentage of total
memory*, so don't set it too high.

1 files changed, 2 insertions, 0 deletions

diff --git a/slabs.h b/slabs.h
index 447033c..1516f86 100644
--- a/slabs.h
+++ b/slabs.h
@@ -10,6 +10,8 @@
 */
 void slabs_init(const size_t limit, const double factor, const bool prealloc, const uint32_t *slab_sizes);
 
+/** Call only during init. Pre-allocates all available memory */
+void slabs_prefill_global(void);
 
 /**
  * Given object size, return id to use when allocating/freeing memory for object