fuse: make the number of max background requests and congestion threshold tunable

The practical values for these limits depend on the design of the
filesystem server so let userspace set them at initialization time.
Signed-off-by: Csaba Henk <csaba@gluster.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/fuse/dev.c

@@ -250,7 +250,7 @@ static void queue_request(struct fuse_conn *fc, struct fuse_req *req)
 
 static void flush_bg_queue(struct fuse_conn *fc)
 {
-	while (fc->active_background < FUSE_MAX_BACKGROUND &&
+	while (fc->active_background < fc->max_background &&
 	       !list_empty(&fc->bg_queue)) {
 		struct fuse_req *req;
 
@@ -280,11 +280,11 @@ __releases(&fc->lock)
 	list_del(&req->intr_entry);
 	req->state = FUSE_REQ_FINISHED;
 	if (req->background) {
-		if (fc->num_background == FUSE_MAX_BACKGROUND) {
+		if (fc->num_background == fc->max_background) {
 			fc->blocked = 0;
 			wake_up_all(&fc->blocked_waitq);
 		}
-		if (fc->num_background == FUSE_CONGESTION_THRESHOLD &&
+		if (fc->num_background == fc->congestion_threshold &&
 		    fc->connected && fc->bdi_initialized) {
 			clear_bdi_congested(&fc->bdi, READ);
 			clear_bdi_congested(&fc->bdi, WRITE);
@@ -410,9 +410,9 @@ static void fuse_request_send_nowait_locked(struct fuse_conn *fc,
 {
 	req->background = 1;
 	fc->num_background++;
-	if (fc->num_background == FUSE_MAX_BACKGROUND)
+	if (fc->num_background == fc->max_background)
 		fc->blocked = 1;
-	if (fc->num_background == FUSE_CONGESTION_THRESHOLD &&
+	if (fc->num_background == fc->congestion_threshold &&
 	    fc->bdi_initialized) {
 		set_bdi_congested(&fc->bdi, READ);
 		set_bdi_congested(&fc->bdi, WRITE);

fs/fuse/fuse_i.h

@@ -25,12 +25,6 @@
 /** Max number of pages that can be used in a single read request */
 #define FUSE_MAX_PAGES_PER_REQ 32
 
-/** Maximum number of outstanding background requests */
-#define FUSE_MAX_BACKGROUND 12
-
-/** Congestion starts at 75% of maximum */
-#define FUSE_CONGESTION_THRESHOLD (FUSE_MAX_BACKGROUND * 75 / 100)
-
 /** Bias for fi->writectr, meaning new writepages must not be sent */
 #define FUSE_NOWRITE INT_MIN
 
@@ -349,6 +343,12 @@ struct fuse_conn {
 	/** rbtree of fuse_files waiting for poll events indexed by ph */
 	struct rb_root polled_files;
 
+	/** Maximum number of outstanding background requests */
+	unsigned max_background;
+
+	/** Number of background requests at which congestion starts */
+	unsigned congestion_threshold;
+
 	/** Number of requests currently in the background */
 	unsigned num_background;
 

fs/fuse/inode.c

@@ -32,6 +32,12 @@ DEFINE_MUTEX(fuse_mutex);
 
 #define FUSE_DEFAULT_BLKSIZE 512
 
+/** Maximum number of outstanding background requests */
+#define FUSE_DEFAULT_MAX_BACKGROUND 12
+
+/** Congestion starts at 75% of maximum */
+#define FUSE_DEFAULT_CONGESTION_THRESHOLD (FUSE_DEFAULT_MAX_BACKGROUND * 3 / 4)
+
 struct fuse_mount_data {
 	int fd;
 	unsigned rootmode;
@@ -517,6 +523,8 @@ void fuse_conn_init(struct fuse_conn *fc)
 	INIT_LIST_HEAD(&fc->bg_queue);
 	INIT_LIST_HEAD(&fc->entry);
 	atomic_set(&fc->num_waiting, 0);
+	fc->max_background = FUSE_DEFAULT_MAX_BACKGROUND;
+	fc->congestion_threshold = FUSE_DEFAULT_CONGESTION_THRESHOLD;
 	fc->khctr = 0;
 	fc->polled_files = RB_ROOT;
 	fc->reqctr = 0;
@@ -736,6 +744,12 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
 	else {
 		unsigned long ra_pages;
 
+		if (arg->minor >= 13) {
+			if (arg->max_background)
+				fc->max_background = arg->max_background;
+			if (arg->congestion_threshold)
+				fc->congestion_threshold = arg->congestion_threshold;
+		}
 		if (arg->minor >= 6) {
 			ra_pages = arg->max_readahead / PAGE_CACHE_SIZE;
 			if (arg->flags & FUSE_ASYNC_READ)

include/linux/fuse.h

@@ -30,6 +30,10 @@
  *  - add umask flag to input argument of open, mknod and mkdir
  *  - add notification messages for invalidation of inodes and
  *    directory entries
+ *
+ * 7.13
+ *  - make max number of background requests and congestion threshold
+ *    tunables
  */
 
 #ifndef _LINUX_FUSE_H
@@ -41,7 +45,7 @@
 #define FUSE_KERNEL_VERSION 7
 
 /** Minor version number of this interface */
-#define FUSE_KERNEL_MINOR_VERSION 12
+#define FUSE_KERNEL_MINOR_VERSION 13
 
 /** The node ID of the root inode */
 #define FUSE_ROOT_ID 1
@@ -427,7 +431,8 @@ struct fuse_init_out {
 	__u32	minor;
 	__u32	max_readahead;
 	__u32	flags;
-	__u32	unused;
+	__u16   max_background;
+	__u16   congestion_threshold;
 	__u32	max_write;
 };