Re: [PATCH 3/4] btrfs: remove redundant csum buffer in btrfs_io_bio

[Nikolay Borisov <nborisov@suse.com>]

On 22.11.18 г. 18:16 ч., David Sterba wrote:
> The io_bio tracks checksums and has an inline buffer or an allocated
> one. And there's a third member that points to the right one, but we
> don't need to use an extra pointer for that. Let btrfs_io_bio::csum
> point to the right buffer and check that the inline buffer is not
> accidentally freed.
> 
> This shrinks struct btrfs_io_bio by 8 bytes.
> 
> Signed-off-by: David Sterba <dsterba@suse.com>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>

> ---
>  fs/btrfs/file-item.c | 12 +++++++-----
>  fs/btrfs/volumes.h   |  1 -
>  2 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
> index ba74827beb32..1f2d0a6ab634 100644
> --- a/fs/btrfs/file-item.c
> +++ b/fs/btrfs/file-item.c
> @@ -144,7 +144,10 @@ int btrfs_lookup_file_extent(struct btrfs_trans_handle *trans,
>  
>  static void btrfs_io_bio_endio_readpage(struct btrfs_io_bio *bio, int err)
>  {
> -	kfree(bio->csum_allocated);
> +	if (bio->csum != bio->csum_inline) {
> +		kfree(bio->csum);
> +		bio->csum = NULL;
> +	}
>  }
>  
>  static blk_status_t __btrfs_lookup_bio_sums(struct inode *inode, struct bio *bio,
> @@ -175,13 +178,12 @@ static blk_status_t __btrfs_lookup_bio_sums(struct inode *inode, struct bio *bio
>  	nblocks = bio->bi_iter.bi_size >> inode->i_sb->s_blocksize_bits;
>  	if (!dst) {
>  		if (nblocks * csum_size > BTRFS_BIO_INLINE_CSUM_SIZE) {
> -			btrfs_bio->csum_allocated = kmalloc_array(nblocks,
> -					csum_size, GFP_NOFS);
> -			if (!btrfs_bio->csum_allocated) {
> +			btrfs_bio->csum = kmalloc_array(nblocks, csum_size,
> +							GFP_NOFS);
> +			if (!btrfs_bio->csum) {
>  				btrfs_free_path(path);
>  				return BLK_STS_RESOURCE;
>  			}
> -			btrfs_bio->csum = btrfs_bio->csum_allocated;
>  			btrfs_bio->end_io = btrfs_io_bio_endio_readpage;
>  		} else {
>  			btrfs_bio->csum = btrfs_bio->csum_inline;
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index 1d936ce282c3..9a764f2d462e 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -274,7 +274,6 @@ struct btrfs_io_bio {
>  	u64 logical;
>  	u8 *csum;
>  	u8 csum_inline[BTRFS_BIO_INLINE_CSUM_SIZE];
> -	u8 *csum_allocated;
>  	btrfs_io_bio_end_io_t *end_io;
>  	struct bvec_iter iter;
>  	/*
>