btrfs: Add handler for invalidate page

For btrfs_invalidatepage() and its variant evict_inode_truncate_page(),
there will be pages don't reach disk.
In that case, their reserved space won't be release nor freed by
finish_ordered_io() nor delayed_ref handler.

So we must free their qgroup reserved space, or we will leaking reserved
space again.

So this will patch will call btrfs_qgroup_free_data() for
invalidatepage() and its variant evict_inode_truncate_page().

And due to the nature of new btrfs_qgroup_reserve/free_data() reserved
space will only be reserved or freed once, so for pages which are
already flushed to disk, their reserved space will be released and freed
by delayed_ref handler.

Double free won't be a problem.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/inode.c

@@ -5132,6 +5132,18 @@ static void evict_inode_truncate_pages(struct inode *inode)
 		spin_unlock(&io_tree->lock);
 
 		lock_extent_bits(io_tree, start, end, 0, &cached_state);
+
+		/*
+		 * If still has DELALLOC flag, the extent didn't reach disk,
+		 * and its reserved space won't be freed by delayed_ref.
+		 * So we need to free its reserved space here.
+		 * (Refer to comment in btrfs_invalidatepage, case 2)
+		 *
+		 * Note, end is the bytenr of last byte, so we need + 1 here.
+		 */
+		if (state->state & EXTENT_DELALLOC)
+			btrfs_qgroup_free_data(inode, start, end - start + 1);
+
 		clear_extent_bit(io_tree, start, end,
 				 EXTENT_LOCKED | EXTENT_DIRTY |
 				 EXTENT_DELALLOC | EXTENT_DO_ACCOUNTING |
@@ -8646,6 +8658,18 @@ static void btrfs_invalidatepage(struct page *page, unsigned int offset,
 		}
 	}
 
+	/*
+	 * Qgroup reserved space handler
+	 * Page here will be either
+	 * 1) Already written to disk
+	 *    In this case, its reserved space is released from data rsv map
+	 *    and will be freed by delayed_ref handler finally.
+	 *    So even we call qgroup_free_data(), it won't decrease reserved
+	 *    space.
+	 * 2) Not written to disk
+	 *    This means the reserved space should be freed here.
+	 */
+	btrfs_qgroup_free_data(inode, page_start, PAGE_CACHE_SIZE);
 	if (!inode_evicting) {
 		clear_extent_bit(tree, page_start, page_end,
 				 EXTENT_LOCKED | EXTENT_DIRTY |