rda, glusterd: Change the max of rda-cache-limit to INFINITY

Issue:
The max value of rda-cache-limit is 1GB before this patch.
When parallel-readdir is enabled, there will be many instances of
readdir-ahead, hence the rda-cache-limit depends on the number of
instances. Eg: On a volume with distribute count 4, rda-cache-limit
when parallel-readdir is enabled, will be 4GB instead of 1GB.
Consider a followinf sequence of operations:
- Enable parallel readdir
- Set rda-cache-limit to lets say 3GB
- Disable parallel-readdir, this results in one instance of readdir-ahead
  and the rda-cache-limit will be back to 1GB, but the current value is 3GB
  and hence the mount will stop working as 3GB > max 1GB.

Solution:
To fix this, we can limit the cache to 1GB even when parallel-readdir
is enabled. But there is no necessity to limit the cache to 1GB, it
can be increased if the system has enough resources. Hence getting rid
of the rda-cache-limit max value is more apt. If we just change the
rda-cache-limit max to INFINITY, we will render older(<3.11) clients
broken, when the rda-cache-limit is set to > 1GB (as the older clients
still expect a value < 1GB). To safely change the max value of
rda-cache-limit to INFINITY, add a check in glusted to verify all
the clients are > 3.11 if the value exceeds 1GB.

Change-Id: Id0cdda3b053287b659c7bf511b13db2e45b92032
BUG: 1446516
Signed-off-by: Poornima G <pgurusid@redhat.com>
Reviewed-on: https://review.gluster.org/17338
Smoke: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Atin Mukherjee <amukherj@redhat.com>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/xlators/performance/readdir-ahead/src/readdir-ahead.c b/xlators/performance/readdir-ahead/src/readdir-ahead.c
index 2ffcf25d8a7..4e7f2b9a879 100644
--- a/xlators/performance/readdir-ahead/src/readdir-ahead.c
+++ b/xlators/performance/readdir-ahead/src/readdir-ahead.c
@@ -23,6 +23,7 @@
  * preloads on the directory.
  */
 
+#include <math.h>
 #include "glusterfs.h"
 #include "xlator.h"
 #include "call-stub.h"
@@ -739,7 +740,7 @@ struct volume_options options[] = {
         { .key = {"rda-cache-limit"},
           .type = GF_OPTION_TYPE_SIZET,
           .min = 0,
-          .max = 1 * GF_UNIT_GB,
+          .max = INFINITY,
           .default_value = "10MB",
           .description = "maximum size of cache consumed by readdir-ahead "
                          "xlator. This value is global and total memory "