Commit f66e0209 authored by Filipe Manana's avatar Filipe Manana Committed by David Sterba
Browse files

btrfs: stop reserving excessive space for block group item updates 



Space for block group item updates, necessary after allocating or
deallocating an extent from a block group, is reserved in the delayed
refs block reserve. Currently we do this by incrementing the transaction
handle's delayed_ref_updates counter and then calling
btrfs_update_delayed_refs_rsv(), which will increase the size of the
delayed refs block reserve by an amount that corresponds to the same
amount we use for delayed refs, given by btrfs_calc_delayed_ref_bytes().

That is an excessive amount because it corresponds to the amount of space
needed to insert one item in a btree (btrfs_calc_insert_metadata_size())
times 2 when the free space tree feature is enabled. All we need is an
amount as given by btrfs_calc_metadata_size(), since we only need to
update an existing block group item in the extent tree (or block group
tree if this feature is enabled). By using btrfs_calc_metadata_size() we
will need to reserve 4 times less space when using the free space tree
and 2 times less space when not using it, putting less pressure on space
reservation.

So use helpers to reserve and release space for block group item updates
that use btrfs_calc_metadata_size() for calculation of the space.

Signed-off-by: default avatarFilipe Manana <fdmanana@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 398fb913

fs/btrfs/block-group.c

+7 −5
Original line number Diff line number Diff line
@@ -1286,7 +1286,7 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans, 
	/* Once for the lookup reference */

	btrfs_put_block_group(block_group);

	if (remove_rsv)

		btrfs_delayed_refs_rsv_release(fs_info, 1, 0);

		btrfs_dec_delayed_refs_rsv_bg_updates(fs_info);

	btrfs_free_path(path);

	return ret;

}
@@ -3369,7 +3369,7 @@ int btrfs_start_dirty_block_groups(struct btrfs_trans_handle *trans) 
		if (should_put)

			btrfs_put_block_group(cache);

		if (drop_reserve)

			btrfs_delayed_refs_rsv_release(fs_info, 1, 0);

			btrfs_dec_delayed_refs_rsv_bg_updates(fs_info);

		/*

		 * Avoid blocking other tasks for too long. It might even save

		 * us from writing caches for block groups that are going to be
@@ -3516,7 +3516,7 @@ int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans) 
		/* If its not on the io list, we need to put the block group */

		if (should_put)

			btrfs_put_block_group(cache);

		btrfs_delayed_refs_rsv_release(fs_info, 1, 0);

		btrfs_dec_delayed_refs_rsv_bg_updates(fs_info);

		spin_lock(&cur_trans->dirty_bgs_lock);

	}

	spin_unlock(&cur_trans->dirty_bgs_lock);
@@ -3545,6 +3545,7 @@ int btrfs_update_block_group(struct btrfs_trans_handle *trans, 
	struct btrfs_block_group *cache;

	u64 old_val;

	bool reclaim = false;

	bool bg_already_dirty = true;

	int factor;



	/* Block accounting for super block */
@@ -3613,7 +3614,7 @@ int btrfs_update_block_group(struct btrfs_trans_handle *trans, 
	spin_lock(&trans->transaction->dirty_bgs_lock);

	if (list_empty(&cache->dirty_list)) {

		list_add_tail(&cache->dirty_list, &trans->transaction->dirty_bgs);

		trans->delayed_ref_updates++;

		bg_already_dirty = false;

		btrfs_get_block_group(cache);

	}

	spin_unlock(&trans->transaction->dirty_bgs_lock);
@@ -3633,7 +3634,8 @@ int btrfs_update_block_group(struct btrfs_trans_handle *trans, 
	btrfs_put_block_group(cache);



	/* Modified block groups are accounted for in the delayed_refs_rsv. */

	btrfs_update_delayed_refs_rsv(trans);

	if (!bg_already_dirty)

		btrfs_inc_delayed_refs_rsv_bg_updates(info);



	return 0;

}

fs/btrfs/delayed-ref.c

+35 −0
Original line number Diff line number Diff line
@@ -125,6 +125,41 @@ void btrfs_update_delayed_refs_rsv(struct btrfs_trans_handle *trans) 
	trans->delayed_ref_csum_deletions = 0;

}



/*

 * Adjust the size of the delayed refs block reserve for 1 block group item

 * update.

 */

void btrfs_inc_delayed_refs_rsv_bg_updates(struct btrfs_fs_info *fs_info)

{

	struct btrfs_block_rsv *delayed_rsv = &fs_info->delayed_refs_rsv;



	spin_lock(&delayed_rsv->lock);

	/*

	 * Updating a block group item does not result in new nodes/leaves and

	 * does not require changing the free space tree, only the extent tree

	 * or the block group tree, so this is all we need.

	 */

	delayed_rsv->size += btrfs_calc_metadata_size(fs_info, 1);

	delayed_rsv->full = false;

	spin_unlock(&delayed_rsv->lock);

}



/*

 * Adjust the size of the delayed refs block reserve to release space for 1

 * block group item update.

 */

void btrfs_dec_delayed_refs_rsv_bg_updates(struct btrfs_fs_info *fs_info)

{

	struct btrfs_block_rsv *delayed_rsv = &fs_info->delayed_refs_rsv;

	const u64 num_bytes = btrfs_calc_metadata_size(fs_info, 1);

	u64 released;



	released = btrfs_block_rsv_release(fs_info, delayed_rsv, num_bytes, NULL);

	if (released > 0)

		trace_btrfs_space_reservation(fs_info, "delayed_refs_rsv",

					      0, released, 0);

}



/*

 * Transfer bytes to our delayed refs rsv.

 *

fs/btrfs/delayed-ref.h

+2 −0
Original line number Diff line number Diff line
@@ -436,6 +436,8 @@ int btrfs_check_delayed_seq(struct btrfs_fs_info *fs_info, u64 seq); 


void btrfs_delayed_refs_rsv_release(struct btrfs_fs_info *fs_info, int nr_refs, int nr_csums);

void btrfs_update_delayed_refs_rsv(struct btrfs_trans_handle *trans);

void btrfs_inc_delayed_refs_rsv_bg_updates(struct btrfs_fs_info *fs_info);

void btrfs_dec_delayed_refs_rsv_bg_updates(struct btrfs_fs_info *fs_info);

int btrfs_delayed_refs_rsv_refill(struct btrfs_fs_info *fs_info,

				  enum btrfs_reserve_flush_enum flush);

void btrfs_migrate_to_delayed_refs_rsv(struct btrfs_fs_info *fs_info,

fs/btrfs/disk-io.c

+1 −1
Original line number Diff line number Diff line
@@ -4774,7 +4774,7 @@ void btrfs_cleanup_dirty_bgs(struct btrfs_transaction *cur_trans, 


		spin_unlock(&cur_trans->dirty_bgs_lock);

		btrfs_put_block_group(cache);

		btrfs_delayed_refs_rsv_release(fs_info, 1, 0);

		btrfs_dec_delayed_refs_rsv_bg_updates(fs_info);

		spin_lock(&cur_trans->dirty_bgs_lock);

	}

	spin_unlock(&cur_trans->dirty_bgs_lock);