cifs: tune bdi.ra_pages in accordance with the rsize

Tune bdi.ra_pages to be a multiple of the rsize. This prevents the VFS
from asking for pages that require small reads to satisfy.
Reviewed-and-Tested-by: NPavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: NJeff Layton <jlayton@redhat.com>

fs/cifs/connect.c

@@ -3182,6 +3182,22 @@ cifs_get_volume_info(char *mount_data, const char *devname)
 	return volume_info;
 }
 
+/* make sure ra_pages is a multiple of rsize */
+static inline unsigned int
+cifs_ra_pages(struct cifs_sb_info *cifs_sb)
+{
+	unsigned int reads;
+	unsigned int rsize_pages = cifs_sb->rsize / PAGE_CACHE_SIZE;
+
+	if (rsize_pages >= default_backing_dev_info.ra_pages)
+		return default_backing_dev_info.ra_pages;
+	else if (rsize_pages == 0)
+		return rsize_pages;
+
+	reads = default_backing_dev_info.ra_pages / rsize_pages;
+	return reads * rsize_pages;
+}
+
 int
 cifs_mount(struct cifs_sb_info *cifs_sb, struct smb_vol *volume_info)
 {
@@ -3200,8 +3216,6 @@ cifs_mount(struct cifs_sb_info *cifs_sb, struct smb_vol *volume_info)
 	if (rc)
 		return rc;
 
-	cifs_sb->bdi.ra_pages = default_backing_dev_info.ra_pages;
-
 #ifdef CONFIG_CIFS_DFS_UPCALL
 try_mount_again:
 	/* cleanup activities if we're chasing a referral */
@@ -3269,6 +3283,9 @@ cifs_mount(struct cifs_sb_info *cifs_sb, struct smb_vol *volume_info)
 	cifs_sb->wsize = cifs_negotiate_wsize(tcon, volume_info);
 	cifs_sb->rsize = cifs_negotiate_rsize(tcon, volume_info);
 
+	/* tune readahead according to rsize */
+	cifs_sb->bdi.ra_pages = cifs_ra_pages(cifs_sb);
+
 remote_path_check:
 #ifdef CONFIG_CIFS_DFS_UPCALL
 	/*