dht/rebalance: Crawler performance improvement

 The job of the crawler in rebalance is to fetch files from each
local subvolume and push them to migration queue if it is eligible for
migration. And we do a lookup on the entries received to figure out the
eligibilty. Since, the lookup done is on a local subvolume we receive
linkto files and regular files as well. This requires us to do two lookups.

first: do a lookup on the file to figure out whether it is a linkto file
second: do a lookup on the file to figure out if it should be migrated

Note: The migrator thread also does one lookup for the file before
migration.

Optimization: Remove the lookup done by the crawler. Offload these task
to the migrator threads. For linkto file verification get the stat and
xattr information from readdirp.

So in total we have one lookup instead of three for each entry.

Performance numbers:
Create two node, two brick setup. Created 100000 files. And started
rebalance. Since, there is no add-brick, no files will be migrated and
we will get the crawler performance.

Without patch:
[root@gprfs039 ~]# grs
                                    Node Rebalanced-files          size
scanned      failures       skipped               status  run time in
h:m:s
                               ---------      -----------   -----------
-----------   -----------   -----------         ------------
--------------
                               localhost                0        0Bytes
50070             0             0            completed        0:0:48
                            server2                0        0Bytes
49930             0             0            completed        0:0:44
volume rebalance: test1: success

Total: 48 seconds

WiththecurrentPatch:
[root@gprfs039 mnt]# gluster v rebalance test1 status
                                    Node Rebalanced-files          size
scanned      failures       skipped               status  run time in
h:m:s
                               ---------      -----------   -----------
-----------   -----------   -----------         ------------
--------------
                               localhost                0        0Bytes
50070             0             0            completed        0:0:12
                            server2                0        0Bytes
49930             0             0            completed        0:0:12
volume rebalance: test1: success

Total: 12 seconds

That's 4X speed gain. :)

Updates glusterfs#155
Change-Id: Idc8e5b366e76c54aa40d698876ae62fe1630b6cc
BUG: 1439571
Signed-off-by: Susant Palai <spalai@redhat.com>
Reviewed-on: https://review.gluster.org/15781
Smoke: Gluster Build System <jenkins@build.gluster.org>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Raghavendra G <rgowdapp@redhat.com>

0 files changed, 0 insertions, 0 deletions