md-cache: Add cache invalidation support to invalidate the meta data cache

Problem:
md-cache currently updates its stat in cbks of selected fops.
The default cache time is 1 second, if this is increasd to reap the
benefits of caching, we may end up with stale cache for long time,
as there is no logic yet to notify md-cache of backend changes by
another client.

Solution:
Use the existing upcall mechanism to invalidate the cache.
For this feature to work, "features.cache-invalidation" volume
option should be enabled.

This patch as is doesn't improve any performance, the benifit of the
patch is that it provides coherency for stat cache, hence the cache
timeout can be quite longer which in turn can improve the performance.

Change-Id: I2dbb0afa7b5e4a5a248f910188e0918e02f18692
BUG: 1211863
Signed-off-by: Poornima G <pgurusid@redhat.com>
Reviewed-on: http://review.gluster.org/12951
Smoke: Gluster Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
Reviewed-by: Raghavendra G <rgowdapp@redhat.com>

0 files changed, 0 insertions, 0 deletions