cifs: add attribute cache timeout (actimeo) tunable

Currently, the attribute cache timeout for CIFS is hardcoded to 1 second. This
means that the client might have to issue a QPATHINFO/QFILEINFO call every 1
second to verify if something has changes, which seems too expensive. On the
other hand, if the timeout is hardcoded to a higher value, workloads that
expect strict cache coherency might see unexpected results.

Making attribute cache timeout as a tunable will allow us to make a tradeoff
between performance and cache metadata correctness depending on the
application/workload needs.

Add 'actimeo' tunable that can be used to tune the attribute cache timeout.
The default timeout is set to 1 second. Also, display actimeo option value in
/proc/mounts.

It appears to me that 'actimeo' and the proposed (but not yet merged)
'strictcache' option cannot coexist, so care must be taken that we reset the
other option if one of them is set.

Changes since last post:
   - fix option parsing and handle possible values correcly

Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 32fa4d9b5dbc..bb17ee2ba782 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -105,6 +105,7 @@ struct smb_vol {
         unsigned int wsize;
         bool sockopt_tcp_nodelay:1;
         unsigned short int port;
+        unsigned long actimeo; /* attribute cache timeout (jiffies) */
         char *prepath;
         struct sockaddr_storage srcaddr; /* allow binding to a local IP */
         struct nls_table *local_nls;
@@ -840,6 +841,8 @@ cifs_parse_mount_options(char *options, const char *devname,
         /* default to using server inode numbers where available */
         vol->server_ino = 1;
 
+        vol->actimeo = CIFS_DEF_ACTIMEO;
+
         if (!options)
                 return 1;
 
@@ -1214,6 +1217,16 @@ cifs_parse_mount_options(char *options, const char *devname,
                                         printk(KERN_WARNING "CIFS: server net"
                                         "biosname longer than 15 truncated.\n");
                         }
+                } else if (strnicmp(data, "actimeo", 7) == 0) {
+                        if (value && *value) {
+                                vol->actimeo = HZ * simple_strtoul(value,
+                                                                   &value, 0);
+                                if (vol->actimeo > CIFS_MAX_ACTIMEO) {
+                                        cERROR(1, "CIFS: attribute cache"
+                                                        "timeout too large");
+                                        return 1;
+                                }
+                        }
                 } else if (strnicmp(data, "credentials", 4) == 0) {
                         /* ignore */
                 } else if (strnicmp(data, "version", 3) == 0) {
@@ -2571,6 +2584,8 @@ static void setup_cifs_sb(struct smb_vol *pvolume_info,
         cFYI(1, "file mode: 0x%x  dir mode: 0x%x",
                 cifs_sb->mnt_file_mode, cifs_sb->mnt_dir_mode);
 
+        cifs_sb->actimeo = pvolume_info->actimeo;
+
         if (pvolume_info->noperm)
                 cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_NO_PERM;
         if (pvolume_info->setuids)