ext4: reserve metadata block for every delayed write

Currently we only reserve space (data+metadata) in delayed allocation if we're allocating from new cluster (which is always in non-bigalloc file system) which is ok for data blocks, because we reserve the whole cluster. However we have to reserve metadata for every delayed block we're going to write because every block could potentially require metedata block when we need to grow the extent tree. Signed-off-by: Lukas Czerner <lczerner@redhat.com>
yi-yang · Mar 11, 2013 · 386ad67 · 386ad67
1 parent 232ec87
commit 386ad67
Showing 1 changed file with 61 additions and 2 deletions.
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
@@ -1304,6 +1304,55 @@ static int ext4_journalled_write_end(struct file *file,
 	return ret ? ret : copied;
 }
 
+/*
+ * Reserve a metadata for a single block located at lblock
+ */
+static int ext4_da_reserve_metadata(struct inode *inode, ext4_lblk_t lblock)
+{
+	int retries = 0;
+	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
+	struct ext4_inode_info *ei = EXT4_I(inode);
+	unsigned int md_needed;
+	ext4_lblk_t save_last_lblock;
+	int save_len;
+
+	/*
+	 * recalculate the amount of metadata blocks to reserve
+	 * in order to allocate nrblocks
+	 * worse case is one extent per block
+	 */
+repeat:
+	spin_lock(&ei->i_block_reservation_lock);
+	/*
+	 * ext4_calc_metadata_amount() has side effects, which we have
+	 * to be prepared undo if we fail to claim space.
+	 */
+	save_len = ei->i_da_metadata_calc_len;
+	save_last_lblock = ei->i_da_metadata_calc_last_lblock;
+	md_needed = EXT4_NUM_B2C(sbi,
+				 ext4_calc_metadata_amount(inode, lblock));
+	trace_ext4_da_reserve_space(inode, md_needed);
+
+	/*
+	 * We do still charge estimated metadata to the sb though;
+	 * we cannot afford to run out of free blocks.
+	 */
+	if (ext4_claim_free_clusters(sbi, md_needed, 0)) {
+		ei->i_da_metadata_calc_len = save_len;
+		ei->i_da_metadata_calc_last_lblock = save_last_lblock;
+		spin_unlock(&ei->i_block_reservation_lock);
+		if (ext4_should_retry_alloc(inode->i_sb, &retries)) {
+			cond_resched();
+			goto repeat;
+		}
+		return -ENOSPC;
+	}
+	ei->i_reserved_meta_blocks += md_needed;
+	spin_unlock(&ei->i_block_reservation_lock);
+
+	return 0;       /* success */
+}
+
 /*
  * Reserve a single cluster located at lblock
  */
@@ -1940,15 +1989,25 @@ static int ext4_da_map_blocks(struct inode *inode, sector_t iblock,
 		 * XXX: __block_prepare_write() unmaps passed block,
 		 * is it OK?
 		 */
-		/* If the block was allocated from previously allocated cluster,
-		 * then we dont need to reserve it again. */
+		/*
+		 * If the block was allocated from previously allocated cluster,
+		 * then we don't need to reserve it again. However we still need
+		 * to reserve metadata for every block we're going to write.
+		 */
 		if (!(map->m_flags & EXT4_MAP_FROM_CLUSTER)) {
 			ret = ext4_da_reserve_space(inode, iblock);
 			if (ret) {
 				/* not enough space to reserve */
 				retval = ret;
 				goto out_unlock;
 			}
+		} else {
+			ret = ext4_da_reserve_metadata(inode, iblock);
+			if (ret) {
+				/* not enough space to reserve */
+				retval = ret;
+				goto out_unlock;
+			}
 		}
 
 		ret = ext4_es_insert_extent(inode, map->m_lblk, map->m_len,