ceph: set io_pages bdi hint

This patch sets the io_pages bdi hint based on the rsize mount option.
Without this patch large buffered reads (request size > max readahead)
are processed sequentially in chunks of the readahead size (i.e. read
requests are sent out up to the readahead size, then the
do_generic_file_read() function waits until the first page is received).

With this patch read requests are sent out at once up to the size
specified in the rsize mount option (default: 64 MB).
Signed-off-by: Andreas Gerstmayr <andreas.gerstmayr@catalysts.cc>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Yan, Zheng <zyan@redhat.com>

Documentation/filesystems/ceph.txt

@@ -98,11 +98,10 @@ Mount Options
 	size.
 
   rsize=X
-	Specify the maximum read size in bytes.  By default there is no
-	maximum.
+	Specify the maximum read size in bytes.  Default: 64 MB.
 
   rasize=X
-	Specify the maximum readahead.
+	Specify the maximum readahead.  Default: 8 MB.
 
   mount_timeout=X
 	Specify the timeout value for mount (in seconds), in the case

fs/ceph/super.c

@@ -952,6 +952,14 @@ static int ceph_register_bdi(struct super_block *sb,
 		fsc->backing_dev_info.ra_pages =
 			VM_MAX_READAHEAD * 1024 / PAGE_SIZE;
 
+	if (fsc->mount_options->rsize > fsc->mount_options->rasize &&
+	    fsc->mount_options->rsize >= PAGE_SIZE)
+		fsc->backing_dev_info.io_pages =
+			(fsc->mount_options->rsize + PAGE_SIZE - 1)
+			>> PAGE_SHIFT;
+	else if (fsc->mount_options->rsize == 0)
+		fsc->backing_dev_info.io_pages = ULONG_MAX;
+
 	err = bdi_register(&fsc->backing_dev_info, NULL, "ceph-%ld",
 			   atomic_long_inc_return(&bdi_seq));
 	if (!err)

fs/ceph/super.h

@@ -45,8 +45,8 @@
 #define ceph_test_mount_opt(fsc, opt) \
 	(!!((fsc)->mount_options->flags & CEPH_MOUNT_OPT_##opt))
 
-#define CEPH_RSIZE_DEFAULT             0           /* max read size */
-#define CEPH_RASIZE_DEFAULT            (8192*1024) /* readahead */
+#define CEPH_RSIZE_DEFAULT              (64*1024*1024) /* max read size */
+#define CEPH_RASIZE_DEFAULT             (8192*1024)    /* max readahead */
 #define CEPH_MAX_READDIR_DEFAULT        1024
 #define CEPH_MAX_READDIR_BYTES_DEFAULT  (512*1024)
 #define CEPH_SNAPDIRNAME_DEFAULT        ".snap"