logfs: commit reservations under space pressure

Ensures we only return -ENOSPC when there really is no space.
Signed-off-by: Joern Engel <joern@logfs.org>

fs/logfs/file.c

@@ -161,6 +161,16 @@ static int logfs_writepage(struct page *page, struct writeback_control *wbc)
 
 static void logfs_invalidatepage(struct page *page, unsigned long offset)
 {
+	struct logfs_block *block = logfs_block(page);
+
+	if (block->reserved_bytes) {
+		struct super_block *sb = page->mapping->host->i_sb;
+		struct logfs_super *super = logfs_super(sb);
+
+		super->s_dirty_pages -= block->reserved_bytes;
+		block->ops->free_block(sb, block);
+		BUG_ON(bitmap_weight(block->alias_map, LOGFS_BLOCK_FACTOR));
+	} else
 		move_page_to_btree(page);
 	BUG_ON(PagePrivate(page) || page->private);
 }

fs/logfs/logfs.h

@@ -394,6 +394,7 @@ struct logfs_super {
 	int	 s_lock_count;
 	mempool_t *s_block_pool;		/* struct logfs_block pool */
 	mempool_t *s_shadow_pool;		/* struct logfs_shadow pool */
+	struct list_head s_writeback_list;	/* writeback pages */
 	/*
 	 * Space accounting:
 	 * - s_used_bytes specifies space used to store valid data objects.

fs/logfs/readwrite.c

@@ -1095,17 +1095,25 @@ static int logfs_reserve_bytes(struct inode *inode, int bytes)
 int get_page_reserve(struct inode *inode, struct page *page)
 {
 	struct logfs_super *super = logfs_super(inode->i_sb);
+	struct logfs_block *block = logfs_block(page);
 	int ret;
 
-	if (logfs_block(page) && logfs_block(page)->reserved_bytes)
+	if (block && block->reserved_bytes)
 		return 0;
 
 	logfs_get_wblocks(inode->i_sb, page, WF_LOCK);
-	ret = logfs_reserve_bytes(inode, 6 * LOGFS_MAX_OBJECTSIZE);
+	while ((ret = logfs_reserve_bytes(inode, 6 * LOGFS_MAX_OBJECTSIZE)) &&
+			!list_empty(&super->s_writeback_list)) {
+		block = list_entry(super->s_writeback_list.next,
+				struct logfs_block, alias_list);
+		block->ops->write_block(block);
+	}
 	if (!ret) {
 		alloc_data_block(inode, page);
-		logfs_block(page)->reserved_bytes += 6 * LOGFS_MAX_OBJECTSIZE;
+		block = logfs_block(page);
+		block->reserved_bytes += 6 * LOGFS_MAX_OBJECTSIZE;
 		super->s_dirty_pages += 6 * LOGFS_MAX_OBJECTSIZE;
+		list_move_tail(&block->alias_list, &super->s_writeback_list);
 	}
 	logfs_put_wblocks(inode->i_sb, page, WF_LOCK);
 	return ret;
@@ -2251,6 +2259,7 @@ int logfs_init_rw(struct super_block *sb)
 	int min_fill = 3 * super->s_no_blocks;
 
 	INIT_LIST_HEAD(&super->s_object_alias);
+	INIT_LIST_HEAD(&super->s_writeback_list);
 	mutex_init(&super->s_write_mutex);
 	super->s_block_pool = mempool_create_kmalloc_pool(min_fill,
 			sizeof(struct logfs_block));