Commit 007145ff authored Mar 21, 2023 by Filipe Manana Committed by David Sterba Apr 17, 2023

btrfs: accurately calculate number of delayed refs when flushing

When flushing a limited number of delayed references (FLUSH_DELAYED_REFS_NR
state), we are assuming each delayed reference is holding a number of bytes
matching the needed space for inserting for a single metadata item (the
result of btrfs_calc_insert_metadata_size()). That is not correct when
using the free space tree, as in that case we have to multiply that value
by 2 since we need to touch the free space tree as well. This is the same
computation as we do at btrfs_update_delayed_refs_rsv() and at
btrfs_delayed_refs_rsv_release().

So correct the computation for the amount of delayed references we need to
flush in case we have the free space tree. This does not fix a functional
issue, instead it makes the flush code flush less delayed references, only
the minimum necessary to satisfy a ticket.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent 1d0df22a

fs/btrfs/space-info.c

+25 −1

Original line number	Diff line number	Diff line
		@@ -550,6 +550,30 @@ static inline u64 calc_reclaim_items_nr(struct btrfs_fs_info *fs_info,
		return nr;
		}

		static inline u64 calc_delayed_refs_nr(struct btrfs_fs_info *fs_info,
		u64 to_reclaim)
		{
		u64 bytes;
		u64 nr;

		bytes = btrfs_calc_insert_metadata_size(fs_info, 1);
		/*
		* We have to check the mount option here because we could be enabling
		* the free space tree for the first time and don't have the compat_ro
		* option set yet.
		*
		* We need extra reservations if we have the free space tree because
		* we'll have to modify that tree as well.
		*/
		if (btrfs_test_opt(fs_info, FREE_SPACE_TREE))
		bytes *= 2;

		nr = div64_u64(to_reclaim, bytes);
		if (!nr)
		nr = 1;
		return nr;
		}

		#define EXTENT_SIZE_PER_ITEM SZ_256K

		/*
		@@ -727,7 +751,7 @@ static void flush_space(struct btrfs_fs_info *fs_info,
		break;
		}
		if (state == FLUSH_DELAYED_REFS_NR)
		nr = calc_reclaim_items_nr(fs_info, num_bytes);
		nr = calc_delayed_refs_nr(fs_info, num_bytes);
		else
		nr = 0;
		btrfs_run_delayed_refs(trans, nr);