9p: implement optional loose read cache

While cacheing is generally frowned upon in the 9p world, it has its
place -- particularly in situations where the remote file system is
exclusive and/or read-only.  The vacfs views of venti content addressable
store are a real-world instance of such a situation.  To facilitate higher
performance for these workloads (and eventually use the fscache patches),
we have enabled a "loose" cache mode which does not attempt to maintain
any form of consistency on the page-cache or dcache.  This results in over
two orders of magnitude performance improvement for cacheable block reads
in the Bonnie benchmark.  The more aggressive use of the dcache also seems
to improve metadata operational performance.

Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index d9b561ba5e58..6ad6f192b6e4 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -53,6 +53,8 @@ enum {
         Opt_uname, Opt_remotename,
         /* Options that take no arguments */
         Opt_legacy, Opt_nodevmap, Opt_unix, Opt_tcp, Opt_fd,
+        /* Cache options */
+        Opt_cache_loose,
         /* Error token */
         Opt_err
 };
@@ -76,6 +78,8 @@ static match_table_t tokens = {
         {Opt_fd, "fd"},
         {Opt_legacy, "noextend"},
         {Opt_nodevmap, "nodevmap"},
+        {Opt_cache_loose, "cache=loose"},
+        {Opt_cache_loose, "loose"},
         {Opt_err, NULL}
 };
 
@@ -106,6 +110,7 @@ static void v9fs_parse_options(char *options, struct v9fs_session_info *v9ses)
         v9ses->debug = 0;
         v9ses->rfdno = ~0;
         v9ses->wfdno = ~0;
+        v9ses->cache = 0;
 
         if (!options)
                 return;
@@ -121,7 +126,6 @@ static void v9fs_parse_options(char *options, struct v9fs_session_info *v9ses)
                                         "integer field, but no integer?\n");
                                 continue;
                         }
-
                 }
                 switch (token) {
                 case Opt_port:
@@ -169,6 +173,9 @@ static void v9fs_parse_options(char *options, struct v9fs_session_info *v9ses)
                 case Opt_nodevmap:
                         v9ses->nodev = 1;
                         break;
+                case Opt_cache_loose:
+                        v9ses->cache = CACHE_LOOSE;
+                        break;
                 default:
                         continue;
                 }