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, 16 insertions, 4 deletions

diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index 5cf22134826b..124a085d1f2e 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -504,7 +504,10 @@ v9fs_vfs_create(struct inode *dir, struct dentry *dentry, int mode,
                 goto error;
         }
 
-        dentry->d_op = &v9fs_dentry_operations;
+        if(v9ses->cache)
+                dentry->d_op = &v9fs_cached_dentry_operations;
+        else
+                dentry->d_op = &v9fs_dentry_operations;
         d_instantiate(dentry, inode);
 
         if (nd && nd->flags & LOOKUP_OPEN) {
@@ -589,7 +592,10 @@ static int v9fs_vfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
                 goto error;
         }
 
-        dentry->d_op = &v9fs_dentry_operations;
+        if(v9ses->cache)
+                dentry->d_op = &v9fs_cached_dentry_operations;
+        else
+                dentry->d_op = &v9fs_dentry_operations;
         d_instantiate(dentry, inode);
         return 0;
 
@@ -626,7 +632,6 @@ static struct dentry *v9fs_vfs_lookup(struct inode *dir, struct dentry *dentry,
 
         sb = dir->i_sb;
         v9ses = v9fs_inode2v9ses(dir);
-        dentry->d_op = &v9fs_dentry_operations;
         dirfid = v9fs_fid_lookup(dentry->d_parent);
 
         if(IS_ERR(dirfid))
@@ -697,6 +702,10 @@ static struct dentry *v9fs_vfs_lookup(struct inode *dir, struct dentry *dentry,
 
         fid->qid = fcall->params.rstat.stat.qid;
         v9fs_stat2inode(&fcall->params.rstat.stat, inode, inode->i_sb);
+        if((fid->qid.version)&&(v9ses->cache))
+                dentry->d_op = &v9fs_cached_dentry_operations;
+        else
+                dentry->d_op = &v9fs_dentry_operations;
 
         d_add(dentry, inode);
         kfree(fcall);
@@ -1184,7 +1193,10 @@ static int v9fs_vfs_mkspecial(struct inode *dir, struct dentry *dentry,
                 goto free_vfid;
         }
 
-        dentry->d_op = &v9fs_dentry_operations;
+        if(v9ses->cache)
+                dentry->d_op = &v9fs_cached_dentry_operations;
+        else
+                dentry->d_op = &v9fs_dentry_operations;
         d_instantiate(dentry, inode);
         return 0;