[PATCH] splice: optimize the splice buffer mapping

We don't really need to lock down the pages, just make sure they
are uptodate.

Signed-off-by: Jens Axboe <axboe@suse.de>

1 files changed, 30 insertions, 10 deletions

diff --git a/fs/splice.c b/fs/splice.c
index 8b5efcc906dc..50c43a1e0923 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -84,26 +84,43 @@ static void *page_cache_pipe_buf_map(struct file *file,
                                      struct pipe_buffer *buf)
 {
         struct page *page = buf->page;
-
-        lock_page(page);
+        int err;
 
         if (!PageUptodate(page)) {
-                unlock_page(page);
-                return ERR_PTR(-EIO);
-        }
+                lock_page(page);
+
+                /*
+                 * Page got truncated/unhashed. This will cause a 0-byte
+                 * splice, if this is the first page
+                 */
+                if (!page->mapping) {
+                        err = -ENODATA;
+                        goto error;
+                }
+
+                /*
+                 * uh oh, read-error from disk
+                 */
+                if (!PageUptodate(page)) {
+                        err = -EIO;
+                        goto error;
+                }
 
-        if (!page->mapping) {
+                /*
+                 * page is ok afterall, fall through to mapping
+                 */
                 unlock_page(page);
-                return ERR_PTR(-ENODATA);
         }
 
-        return kmap(buf->page);
+        return kmap(page);
+error:
+        unlock_page(page);
+        return ERR_PTR(err);
 }
 
 static void page_cache_pipe_buf_unmap(struct pipe_inode_info *info,
                                       struct pipe_buffer *buf)
 {
-        unlock_page(buf->page);
         kunmap(buf->page);
 }
 
@@ -379,7 +396,7 @@ static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf,
         int ret;
 
         /*
-         * after this, page will be locked and unmapped
+         * make sure the data in this buffer is uptodate
          */
         src = buf->ops->map(file, info, buf);
         if (IS_ERR(src))
@@ -399,6 +416,9 @@ static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf,
                 if (buf->ops->steal(info, buf))
                         goto find_page;
 
+                /*
+                 * this will also set the page locked
+                 */
                 page = buf->page;
                 if (add_to_page_cache(page, mapping, index, gfp_mask))
                         goto find_page;