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>

fs/cifs/README

@@ -337,6 +337,15 @@ A partial list of the supported mount options follows:
   wsize		default write size (default 57344)
 		maximum wsize currently allowed by CIFS is 57344 (fourteen
 		4096 byte pages)
+  actimeo=n	attribute cache timeout in seconds (default 1 second).
+		After this timeout, the cifs client requests fresh attribute
+		information from the server. This option allows to tune the
+		attribute cache timeout to suit the workload needs. Shorter
+		timeouts mean better the cache coherency, but increased number
+		of calls to the server. Longer timeouts mean reduced number
+		of calls to the server at the expense of less stricter cache
+		coherency checks (i.e. incorrect attribute cache for a short
+		period of time).
   rw		mount the network share read-write (note that the
 		server may still consider the share read-only)
   ro		mount network share read-only

fs/cifs/cifs_fs_sb.h

@@ -48,6 +48,7 @@ struct cifs_sb_info {
 	struct nls_table *local_nls;
 	unsigned int rsize;
 	unsigned int wsize;
+	unsigned long actimeo; /* attribute cache timeout (jiffies) */
 	atomic_t active;
 	uid_t	mnt_uid;
 	gid_t	mnt_gid;

fs/cifs/cifsfs.c

@@ -463,6 +463,8 @@ cifs_show_options(struct seq_file *s, struct vfsmount *m)
 
 	seq_printf(s, ",rsize=%d", cifs_sb->rsize);
 	seq_printf(s, ",wsize=%d", cifs_sb->wsize);
+	/* convert actimeo and display it in seconds */
+		seq_printf(s, ",actimeo=%lu", cifs_sb->actimeo / HZ);
 
 	return 0;
 }

fs/cifs/cifsglob.h

@@ -44,6 +44,16 @@
 
 #define CIFS_MIN_RCV_POOL 4
 
+/*
+ * default attribute cache timeout (jiffies)
+ */
+#define CIFS_DEF_ACTIMEO (1 * HZ)
+
+/*
+ * max attribute cache timeout (jiffies) - 2^30
+ */
+#define CIFS_MAX_ACTIMEO (1 << 30)
+
 /*
  * MAX_REQ is the maximum number of requests that WE will send
  * on one socket concurrently. It also matches the most common

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)

fs/cifs/inode.c

@@ -1653,6 +1653,7 @@ static bool
 cifs_inode_needs_reval(struct inode *inode)
 {
 	struct cifsInodeInfo *cifs_i = CIFS_I(inode);
+	struct cifs_sb_info *cifs_sb = CIFS_SB(inode->i_sb);
 
 	if (cifs_i->clientCanCacheRead)
 		return false;
@@ -1663,12 +1664,12 @@ cifs_inode_needs_reval(struct inode *inode)
 	if (cifs_i->time == 0)
 		return true;
 
-	/* FIXME: the actimeo should be tunable */
-	if (time_after_eq(jiffies, cifs_i->time + HZ))
+	if (!time_in_range(jiffies, cifs_i->time,
+				cifs_i->time + cifs_sb->actimeo))
 		return true;
 
 	/* hardlinked files w/ noserverino get "special" treatment */
-	if (!(CIFS_SB(inode->i_sb)->mnt_cifs_flags & CIFS_MOUNT_SERVER_INUM) &&
+	if (!(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_SERVER_INUM) &&
 	    S_ISREG(inode->i_mode) && inode->i_nlink != 1)
 		return true;