UBIFS: do not allocate too much

Bulk-read allocates 128KiB or more using kmalloc. The allocation
starts failing often when the memory gets fragmented. UBIFS still
works fine in this case, because it falls-back to standard
(non-optimized) read method, though. This patch teaches bulk-read
to allocate exactly the amount of memory it needs, instead of
allocating 128KiB every time.

This patch is also a preparation to the further fix where we'll
have a pre-allocated bulk-read buffer as well. For example, now
the @bu object is prepared in 'ubifs_bulk_read()', so we could
path either pre-allocated or allocated information to
'ubifs_do_bulk_read()' later. Or teaching 'ubifs_do_bulk_read()'
not to allocate 'bu->buf' if it is already there.

Signed-off-by: Artem Bityutskiy <[e-mail]>

fs/ubifs/file.c

···
 /**
  * ubifs_do_bulk_read - do bulk-read.
  * @c: UBIFS file-system description object
- * @page1: first page
+ * @bu: bulk-read information
+ * @page1: first page to read
  *
  * This function returns %1 if the bulk-read is done, otherwise %0 is returned.
  */
-static int ubifs_do_bulk_read(struct ubifs_info *c, struct page *page1)
+static int ubifs_do_bulk_read(struct ubifs_info *c, struct bu_info *bu,
+			      struct page *page1)
 {
 	pgoff_t offset = page1->index, end_index;
 	struct address_space *mapping = page1->mapping;
 	struct inode *inode = mapping->host;
 	struct ubifs_inode *ui = ubifs_inode(inode);
-	struct bu_info *bu;
 	int err, page_idx, page_cnt, ret = 0, n = 0;
+	int allocate = bu->buf ? 0 : 1;
 	loff_t isize;
-
-	bu = kmalloc(sizeof(struct bu_info), GFP_NOFS | __GFP_NOWARN);
-	if (!bu)
-		return 0;
-
-	bu->buf_len = c->bulk_read_buf_size;
-	bu->buf = kmalloc(bu->buf_len, GFP_NOFS | __GFP_NOWARN);
-	if (!bu->buf)
-		goto out_free;
-
-	data_key_init(c, &bu->key, inode->i_ino,
-		      offset << UBIFS_BLOCKS_PER_PAGE_SHIFT);
 
 	err = ubifs_tnc_get_bu_keys(c, bu);
 	if (err)
···
 		 * together. If all the pages were like this, bulk-read would
 		 * reduce performance, so we turn it off for a while.
 		 */
-		ui->read_in_a_row = 0;
-		ui->bulk_read = 0;
-		goto out_free;
+		goto out_bu_off;
 	}
 
 	if (bu->cnt) {
+		if (allocate) {
+			/*
+			 * Allocate bulk-read buffer depending on how many data
+			 * nodes we are going to read.
+			 */
+			bu->buf_len = bu->zbranch[bu->cnt - 1].offs +
+				      bu->zbranch[bu->cnt - 1].len -
+				      bu->zbranch[0].offs;
+			ubifs_assert(bu->buf_len > 0);
+			ubifs_assert(bu->buf_len <= c->leb_size);
+			bu->buf = kmalloc(bu->buf_len, GFP_NOFS | __GFP_NOWARN);
+			if (!bu->buf)
+				goto out_bu_off;
+		}
+
 		err = ubifs_tnc_bulk_read(c, bu);
 		if (err)
 			goto out_warn;
···
 	ui->last_page_read = offset + page_idx - 1;
 
 out_free:
-	kfree(bu->buf);
-	kfree(bu);
+	if (allocate)
+		kfree(bu->buf);
 	return ret;
 
 out_warn:
 	ubifs_warn("ignoring error %d and skipping bulk-read", err);
+	goto out_free;
+
+out_bu_off:
+	ui->read_in_a_row = ui->bulk_read = 0;
 	goto out_free;
 }
 
···
 	struct ubifs_info *c = inode->i_sb->s_fs_info;
 	struct ubifs_inode *ui = ubifs_inode(inode);
 	pgoff_t index = page->index, last_page_read = ui->last_page_read;
-	int ret = 0;
+	struct bu_info *bu;
+	int err = 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.
 	 */
 	if (!mutex_trylock(&ui->ui_mutex))
 		return 0;
+
 	if (index != last_page_read + 1) {
 		/* Turn off bulk-read if we stop reading sequentially */
 		ui->read_in_a_row = 1;
···
 			ui->bulk_read = 0;
 		goto out_unlock;
 	}
+
 	if (!ui->bulk_read) {
 		ui->read_in_a_row += 1;
 		if (ui->read_in_a_row < 3)
···
 		/* Three reads in a row, so switch on bulk-read */
 		ui->bulk_read = 1;
 	}
-	ret = ubifs_do_bulk_read(c, page);
+
+	bu = kmalloc(sizeof(struct bu_info), GFP_NOFS | __GFP_NOWARN);
+	if (!bu)
+		return 0;
+
+	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);
+
 out_unlock:
 	mutex_unlock(&ui->ui_mutex);
-	return ret;
+	return err;
 }
 
 static int ubifs_readpage(struct file *file, struct page *page)

fs/ubifs/super.c

···
 	c->leb_overhead = c->leb_size % UBIFS_MAX_DATA_NODE_SZ;
 
 	/* Buffer size for bulk-reads */
-	c->bulk_read_buf_size = UBIFS_MAX_BULK_READ * UBIFS_MAX_DATA_NODE_SZ;
-	if (c->bulk_read_buf_size > c->leb_size)
-		c->bulk_read_buf_size = c->leb_size;
-	if (c->bulk_read_buf_size > UBIFS_KMALLOC_OK) {
+	c->max_bu_buf_len = UBIFS_MAX_BULK_READ * UBIFS_MAX_DATA_NODE_SZ;
+	if (c->max_bu_buf_len > c->leb_size)
+		c->max_bu_buf_len = c->leb_size;
+	if (c->max_bu_buf_len > UBIFS_KMALLOC_OK) {
 		/* Check if we can kmalloc that much */
-		void *try = kmalloc(c->bulk_read_buf_size,
+		void *try = kmalloc(c->max_bu_buf_len,
 				    GFP_KERNEL | __GFP_NOWARN);
 		kfree(try);
 		if (!try)
-			c->bulk_read_buf_size = UBIFS_KMALLOC_OK;
+			c->max_bu_buf_len = UBIFS_KMALLOC_OK;
 	}
 	return 0;
 }

fs/ubifs/tnc.c

···
  * @bu: bulk-read parameters and results
  *
  * Lookup consecutive data node keys for the same inode that reside
- * consecutively in the same LEB.
+ * consecutively in the same LEB. This function returns zero in case of success
+ * and a negative error code in case of failure.
+ *
+ * Note, if the bulk-read buffer length (@bu->buf_len) is known, this function
+ * makes sure bulk-read nodes fit the buffer. Otherwise, this function prepares
+ * maxumum possible amount of nodes for bulk-read.
  */
 int ubifs_tnc_get_bu_keys(struct ubifs_info *c, struct bu_info *bu)
 {

fs/ubifs/ubifs.h

···
  * @mst_node: master node
  * @mst_offs: offset of valid master node
  * @mst_mutex: protects the master node area, @mst_node, and @mst_offs
- * @bulk_read_buf_size: buffer size for bulk-reads
+ * @max_bu_buf_len: maximum bulk-read buffer length
  *
  * @log_lebs: number of logical eraseblocks in the log
  * @log_bytes: log size in bytes
···
 	struct ubifs_mst_node *mst_node;
 	int mst_offs;
 	struct mutex mst_mutex;
-	int bulk_read_buf_size;
+	int max_bu_buf_len;
 
 	int log_lebs;
 	long long log_bytes;