Commit feefe1f4 authored by Filipe Manana's avatar Filipe Manana Committed by David Sterba
Browse files

btrfs: don't reserve space for checksums when writing to nocow files 



Currently when doing a write to a file we always reserve metadata space
for inserting data checksums. However we don't need to do it if we have
a nodatacow file (-o nodatacow mount option or chattr +C) or if checksums
are disabled (-o nodatasum mount option), as in that case we are only
adding unnecessary pressure to metadata reservations.

For example on x86_64, with the default node size of 16K, a 4K buffered
write into a nodatacow file is reserving 655360 bytes of metadata space,
as it's accounting for checksums. After this change, which stops reserving
space for checksums if we have a nodatacow file or checksums are disabled,
we only need to reserve 393216 bytes of metadata.

CC: stable@vger.kernel.org # 6.1+
Signed-off-by: default avatarFilipe Manana <fdmanana@suse.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 12c5128f

fs/btrfs/delalloc-space.c

+19 −10
Original line number Diff line number Diff line
@@ -245,7 +245,6 @@ static void btrfs_calculate_inode_block_rsv_size(struct btrfs_fs_info *fs_info, 
	struct btrfs_block_rsv *block_rsv = &inode->block_rsv;

	u64 reserve_size = 0;

	u64 qgroup_rsv_size = 0;

	u64 csum_leaves;

	unsigned outstanding_extents;



	lockdep_assert_held(&inode->lock);
@@ -260,10 +259,12 @@ static void btrfs_calculate_inode_block_rsv_size(struct btrfs_fs_info *fs_info, 
						outstanding_extents);

		reserve_size += btrfs_calc_metadata_size(fs_info, 1);

	}

	csum_leaves = btrfs_csum_bytes_to_leaves(fs_info,

						 inode->csum_bytes);

	reserve_size += btrfs_calc_insert_metadata_size(fs_info,

							csum_leaves);

	if (!(inode->flags & BTRFS_INODE_NODATASUM)) {

		u64 csum_leaves;



		csum_leaves = btrfs_csum_bytes_to_leaves(fs_info, inode->csum_bytes);

		reserve_size += btrfs_calc_insert_metadata_size(fs_info, csum_leaves);

	}

	/*

	 * For qgroup rsv, the calculation is very simple:

	 * account one nodesize for each outstanding extent
@@ -278,14 +279,20 @@ static void btrfs_calculate_inode_block_rsv_size(struct btrfs_fs_info *fs_info, 
	spin_unlock(&block_rsv->lock);

}



static void calc_inode_reservations(struct btrfs_fs_info *fs_info,

static void calc_inode_reservations(struct btrfs_inode *inode,

				    u64 num_bytes, u64 disk_num_bytes,

				    u64 *meta_reserve, u64 *qgroup_reserve)

{

	struct btrfs_fs_info *fs_info = inode->root->fs_info;

	u64 nr_extents = count_max_extents(fs_info, num_bytes);

	u64 csum_leaves = btrfs_csum_bytes_to_leaves(fs_info, disk_num_bytes);

	u64 csum_leaves;

	u64 inode_update = btrfs_calc_metadata_size(fs_info, 1);



	if (inode->flags & BTRFS_INODE_NODATASUM)

		csum_leaves = 0;

	else

		csum_leaves = btrfs_csum_bytes_to_leaves(fs_info, disk_num_bytes);



	*meta_reserve = btrfs_calc_insert_metadata_size(fs_info,

						nr_extents + csum_leaves);
@@ -337,7 +344,7 @@ int btrfs_delalloc_reserve_metadata(struct btrfs_inode *inode, u64 num_bytes, 
	 * everything out and try again, which is bad.  This way we just

	 * over-reserve slightly, and clean up the mess when we are done.

	 */

	calc_inode_reservations(fs_info, num_bytes, disk_num_bytes,

	calc_inode_reservations(inode, num_bytes, disk_num_bytes,

				&meta_reserve, &qgroup_reserve);

	ret = btrfs_qgroup_reserve_meta_prealloc(root, qgroup_reserve, true,

						 noflush);
@@ -359,6 +366,7 @@ int btrfs_delalloc_reserve_metadata(struct btrfs_inode *inode, u64 num_bytes, 
	nr_extents = count_max_extents(fs_info, num_bytes);

	spin_lock(&inode->lock);

	btrfs_mod_outstanding_extents(inode, nr_extents);

	if (!(inode->flags & BTRFS_INODE_NODATASUM))

		inode->csum_bytes += disk_num_bytes;

	btrfs_calculate_inode_block_rsv_size(fs_info, inode);

	spin_unlock(&inode->lock);
@@ -393,6 +401,7 @@ void btrfs_delalloc_release_metadata(struct btrfs_inode *inode, u64 num_bytes, 


	num_bytes = ALIGN(num_bytes, fs_info->sectorsize);

	spin_lock(&inode->lock);

	if (!(inode->flags & BTRFS_INODE_NODATASUM))

		inode->csum_bytes -= num_bytes;

	btrfs_calculate_inode_block_rsv_size(fs_info, inode);

	spin_unlock(&inode->lock);