Btrfs: do not overcommit if we don't have enough space for global rsv (96f1bb57) · Commits · 戴 / test

Because of how little we allocate chunks now we can get really tight on metadata space before we will allocate a new chunk. This resulted in being unable to add device extents when allocating a new metadata chunk as we did not have enough space. This is because we were allowed to overcommit too much metadata without actually making sure we had enough space to make allocations. The idea behind overcommit is that we are allowed to say "sure you can have that reservation" when most of the free space is occupied by reservations, not actual allocations. But in this case where a majority of the total space is in use by actual allocations we can screw ourselves by not being able to make real allocations when it matters. So make sure we have enough real space for our global reserve, and if not then don't allow overcommitting. Thanks, Reported-and-tested-by:

Jim Schutt <jaschut@sandia.gov> Signed-off-by:

Josef Bacik <jbacik@fusionio.com>

fs/btrfs/extent-tree.c

+19 −2

Original line number	Diff line number	Diff line
		@@ -3672,13 +3672,30 @@ static int can_overcommit(struct btrfs_root *root,
		struct btrfs_space_info *space_info, u64 bytes,
		enum btrfs_reserve_flush_enum flush)
		{
		struct btrfs_block_rsv *global_rsv = &root->fs_info->global_block_rsv;
		u64 profile = btrfs_get_alloc_profile(root, 0);
		u64 rsv_size = 0;
		u64 avail;
		u64 used;

		used = space_info->bytes_used + space_info->bytes_reserved +
		space_info->bytes_pinned + space_info->bytes_readonly +
		space_info->bytes_may_use;
		space_info->bytes_pinned + space_info->bytes_readonly;

		spin_lock(&global_rsv->lock);
		rsv_size = global_rsv->size;
		spin_unlock(&global_rsv->lock);

		/*
		* We only want to allow over committing if we have lots of actual space
		* free, but if we don't have enough space to handle the global reserve
		* space then we could end up having a real enospc problem when trying
		* to allocate a chunk or some other such important allocation.
		*/
		rsv_size <<= 1;
		if (used + rsv_size >= space_info->total_bytes)
		return 0;

		used += space_info->bytes_may_use;

		spin_lock(&root->fs_info->free_chunk_lock);
		avail = root->fs_info->free_chunk_space;

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