fuse: allow batching of FORGET requests

Terje Malmedal reports that a fuse filesystem with 32 million inodes
on a machine with lots of memory can take up to 30 minutes to process
FORGET requests when all those inodes are evicted from the icache.

To solve this, create a BATCH_FORGET request that allows up to about
8000 FORGET requests to be sent in a single message.

This request is only sent if userspace supports interface version 7.16
or later, otherwise fall back to sending individual FORGET messages.

Reported-by: Terje Malmedal <terje.malmedal@usit.uio.no>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

1 files changed, 81 insertions, 11 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index fed65303eeeb..cf8d28d1fbad 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -254,8 +254,8 @@ static void queue_request(struct fuse_conn *fc, struct fuse_req *req)
 void fuse_queue_forget(struct fuse_conn *fc, struct fuse_forget_link *forget,
                        u64 nodeid, u64 nlookup)
 {
-        forget->nodeid = nodeid;
-        forget->nlookup = nlookup;
+        forget->forget_one.nodeid = nodeid;
+        forget->forget_one.nlookup = nlookup;
 
         spin_lock(&fc->lock);
         fc->forget_list_tail->next = forget;
@@ -974,15 +974,26 @@ __releases(fc->lock)
         return err ? err : reqsize;
 }
 
-static struct fuse_forget_link *dequeue_forget(struct fuse_conn *fc)
+static struct fuse_forget_link *dequeue_forget(struct fuse_conn *fc,
+                                               unsigned max,
+                                               unsigned *countp)
 {
-        struct fuse_forget_link *forget = fc->forget_list_head.next;
+        struct fuse_forget_link *head = fc->forget_list_head.next;
+        struct fuse_forget_link **newhead = &head;
+        unsigned count;
 
-        fc->forget_list_head.next = forget->next;
+        for (count = 0; *newhead != NULL && count < max; count++)
+                newhead = &(*newhead)->next;
+
+        fc->forget_list_head.next = *newhead;
+        *newhead = NULL;
         if (fc->forget_list_head.next == NULL)
                 fc->forget_list_tail = &fc->forget_list_head;
 
-        return forget;
+        if (countp != NULL)
+                *countp = count;
+
+        return head;
 }
 
 static int fuse_read_single_forget(struct fuse_conn *fc,
@@ -991,13 +1002,13 @@ static int fuse_read_single_forget(struct fuse_conn *fc,
 __releases(fc->lock)
 {
         int err;
-        struct fuse_forget_link *forget = dequeue_forget(fc);
+        struct fuse_forget_link *forget = dequeue_forget(fc, 1, NULL);
         struct fuse_forget_in arg = {
-                .nlookup = forget->nlookup,
+                .nlookup = forget->forget_one.nlookup,
         };
         struct fuse_in_header ih = {
                 .opcode = FUSE_FORGET,
-                .nodeid = forget->nodeid,
+                .nodeid = forget->forget_one.nodeid,
                 .unique = fuse_get_unique(fc),
                 .len = sizeof(ih) + sizeof(arg),
         };
@@ -1018,6 +1029,65 @@ __releases(fc->lock)
         return ih.len;
 }
 
+static int fuse_read_batch_forget(struct fuse_conn *fc,
+                                   struct fuse_copy_state *cs, size_t nbytes)
+__releases(fc->lock)
+{
+        int err;
+        unsigned max_forgets;
+        unsigned count;
+        struct fuse_forget_link *head;
+        struct fuse_batch_forget_in arg = { .count = 0 };
+        struct fuse_in_header ih = {
+                .opcode = FUSE_BATCH_FORGET,
+                .unique = fuse_get_unique(fc),
+                .len = sizeof(ih) + sizeof(arg),
+        };
+
+        if (nbytes < ih.len) {
+                spin_unlock(&fc->lock);
+                return -EINVAL;
+        }
+
+        max_forgets = (nbytes - ih.len) / sizeof(struct fuse_forget_one);
+        head = dequeue_forget(fc, max_forgets, &count);
+        spin_unlock(&fc->lock);
+
+        arg.count = count;
+        ih.len += count * sizeof(struct fuse_forget_one);
+        err = fuse_copy_one(cs, &ih, sizeof(ih));
+        if (!err)
+                err = fuse_copy_one(cs, &arg, sizeof(arg));
+
+        while (head) {
+                struct fuse_forget_link *forget = head;
+
+                if (!err) {
+                        err = fuse_copy_one(cs, &forget->forget_one,
+                                            sizeof(forget->forget_one));
+                }
+                head = forget->next;
+                kfree(forget);
+        }
+
+        fuse_copy_finish(cs);
+
+        if (err)
+                return err;
+
+        return ih.len;
+}
+
+static int fuse_read_forget(struct fuse_conn *fc, struct fuse_copy_state *cs,
+                            size_t nbytes)
+__releases(fc->lock)
+{
+        if (fc->minor < 16 || fc->forget_list_head.next->next == NULL)
+                return fuse_read_single_forget(fc, cs, nbytes);
+        else
+                return fuse_read_batch_forget(fc, cs, nbytes);
+}
+
 /*
  * Read a single request into the userspace filesystem's buffer.  This
  * function waits until a request is available, then removes it from
@@ -1058,7 +1128,7 @@ static ssize_t fuse_dev_do_read(struct fuse_conn *fc, struct file *file,
 
         if (forget_pending(fc)) {
                 if (list_empty(&fc->pending) || fc->forget_batch-- > 0)
-                        return fuse_read_single_forget(fc, cs, nbytes);
+                        return fuse_read_forget(fc, cs, nbytes);
 
                 if (fc->forget_batch <= -8)
                         fc->forget_batch = 16;
@@ -1837,7 +1907,7 @@ __acquires(fc->lock)
         end_requests(fc, &fc->pending);
         end_requests(fc, &fc->processing);
         while (forget_pending(fc))
-                kfree(dequeue_forget(fc));
+                kfree(dequeue_forget(fc, 1, NULL));
 }
 
 /*