rebalance: Introducing local crawl and parallel migration

The current patch address two part of the design proposed.
1. Rebalance multiple files in parallel
2. Crawl only bricks that belong to the current node

Brief design explanation for the above two points.

1. Rebalance multiple files in parallel:
   -------------------------------------
The existing rebalance engine is single threaded. Hence, introduced
multiple threads which will be running parallel to the crawler. The
current rebalance migration is converted to a "Producer-Consumer"
frame work.

Where Producer is : Crawler
      Consumer is : Migrating Threads

Crawler: Crawler is the main thread. The job of the crawler is now
limited to fix-layout of each directory and add the files which are
eligible for the migration to a global queue in a round robin manner
so that we will use all the disk resources efficiently. Hence, the
crawler will not be "blocked" by migration process.

Producer: Producer will monitor the global queue. If any file is
added to this queue, it will dqueue that entry and migrate the file.
Currently 20 migration threads are spawned at the beginning of the
rebalance process. Hence, multiple file migration happens in parallel.

2. Crawl only bricks that belong to the current node:
   --------------------------------------------------
As rebalance process is spawned per node, it migrates only the files
that belongs to it's own node for the sake of load balancing. But it
also reads entries from the whole cluster, which is not necessary as
readdir hits other nodes.

New Design:
        As part of the new design the rebalancer decides the subvols
that are local to the rebalancer node by checking the node-uuid of
root directory prior to the crawler starts. Hence, readdir won't hit
the whole cluster  as it has already the context of local subvols and
also node-uuid request for each file can be avoided. This makes the
rebalance process "more scalable".

Change-Id: I6f1b44086a09df8ca23935fd213509c70cc0c050
BUG: 1217381
Signed-off-by: Susant Palai <spalai@redhat.com>
Reviewed-on: http://review.gluster.org/10466
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Tested-by: NetBSD Build System
Reviewed-by: N Balachandran <nbalacha@redhat.com>

2 files changed, 3 insertions, 0 deletions

diff --git a/libglusterfs/src/glusterfs.h b/libglusterfs/src/glusterfs.h
index 2923aeb4aa4..f6c10e99ef9 100644
--- a/libglusterfs/src/glusterfs.h
+++ b/libglusterfs/src/glusterfs.h
@@ -83,6 +83,7 @@
 #define GF_XATTR_CLRLK_CMD      "glusterfs.clrlk"
 #define GF_XATTR_PATHINFO_KEY   "trusted.glusterfs.pathinfo"
 #define GF_XATTR_NODE_UUID_KEY  "trusted.glusterfs.node-uuid"
+#define GF_REBAL_FIND_LOCAL_SUBVOL "glusterfs.find-local-subvol"
 #define GF_XATTR_VOL_ID_KEY   "trusted.glusterfs.volume-id"
 #define GF_XATTR_LOCKINFO_KEY   "trusted.glusterfs.lockinfo"
 #define GF_XATTR_GET_REAL_FILENAME_KEY "glusterfs.get_real_filename:"
diff --git a/libglusterfs/src/mem-types.h b/libglusterfs/src/mem-types.h
index fc06d52239b..a77998e8a63 100644
--- a/libglusterfs/src/mem-types.h
+++ b/libglusterfs/src/mem-types.h
@@ -150,6 +150,8 @@ enum gf_common_mem_types_ {
         gf_common_mt_nfs_exports          = 131,
         gf_common_mt_gf_brick_spec_t      = 132,
         gf_common_mt_gf_timer_entry_t     = 133,
+        gf_common_mt_int                  = 134,
+        gf_common_mt_pointer              = 135,
         gf_common_mt_end
 };
 #endif