UBIFS: pre-allocate bulk-read buffer

To avoid memory allocation failure during bulk-read, pre-allocate
a bulk-read buffer, so that if there is only one bulk-reader at
a time, it would just use the pre-allocated buffer and would not
do any memory allocation. However, if there are more than 1 bulk-
reader, then only one reader would use the pre-allocated buffer,
while the other reader would allocate the buffer for itself.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

1 files changed, 22 insertions, 9 deletions

diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index 0c5c27d63f6e..2624411d9758 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -811,15 +811,15 @@ static int ubifs_bulk_read(struct page *page)
 	struct ubifs_inode *ui = ubifs_inode(inode);
 	pgoff_t index = page->index, last_page_read = ui->last_page_read;
 	struct bu_info *bu;
-	int err = 0;
+	int err = 0, allocated = 0;
 
 	ui->last_page_read = index;
 	if (!c->bulk_read)
 		return 0;
 
 	/*
-	 * Bulk-read is protected by ui_mutex, but it is an optimization, so
-	 * don't bother if we cannot lock the mutex.
+	 * Bulk-read is protected by @ui->ui_mutex, but it is an optimization,
+	 * so don't bother if we cannot lock the mutex.
 	 */
 	if (!mutex_trylock(&ui->ui_mutex))
 		return 0;
@@ -840,17 +840,30 @@ static int ubifs_bulk_read(struct page *page)
 		ui->bulk_read = 1;
 	}
 
-	bu = kmalloc(sizeof(struct bu_info), GFP_NOFS | __GFP_NOWARN);
-	if (!bu)
-		return 0;
+	/*
+	 * If possible, try to use pre-allocated bulk-read information, which
+	 * is protected by @c->bu_mutex.
+	 */
+	if (mutex_trylock(&c->bu_mutex))
+		bu = &c->bu;
+	else {
+		bu = kmalloc(sizeof(struct bu_info), GFP_NOFS | __GFP_NOWARN);
+		if (!bu)
+			goto out_unlock;
+
+		bu->buf = NULL;
+		allocated = 1;
+	}
 
-	bu->buf = NULL;
 	bu->buf_len = c->max_bu_buf_len;
 	data_key_init(c, &bu->key, inode->i_ino,
 		      page->index << UBIFS_BLOCKS_PER_PAGE_SHIFT);
-
 	err = ubifs_do_bulk_read(c, bu, page);
-	kfree(bu);
+
+	if (!allocated)
+		mutex_unlock(&c->bu_mutex);
+	else
+		kfree(bu);
 
 out_unlock:
 	mutex_unlock(&ui->ui_mutex);