Re: [PATCH 2/6] btrfs: optimize simple reads in btrfsic_map_block

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2023/5/31 12:17, Christoph Hellwig wrote:
> Pass a smap into __btrfs_map_block so that the usual case of a read that
> doesn't require parity raid recovery doesn't need an extra memory
> allocation for the btrfs_io_context.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Qu Wenruo <wqu@suse.com>

I'm more curious on whether the check-integrity feature is still under
heavy usage.

It's from old time where we don't have a lot of sanity checks, but
nowadays it looks less worthy and can cause extra burden to maintain.

Thanks,
Qu
> ---
>   fs/btrfs/check-integrity.c | 19 ++++++++++++-------
>   1 file changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
> index b4408037b823c5..fe15367000141a 100644
> --- a/fs/btrfs/check-integrity.c
> +++ b/fs/btrfs/check-integrity.c
> @@ -1459,13 +1459,13 @@ static int btrfsic_map_block(struct btrfsic_state *state, u64 bytenr, u32 len,
>   	struct btrfs_fs_info *fs_info = state->fs_info;
>   	int ret;
>   	u64 length;
> -	struct btrfs_io_context *multi = NULL;
> +	struct btrfs_io_context *bioc = NULL;
> +	struct btrfs_io_stripe smap, *map;
>   	struct btrfs_device *device;
>
>   	length = len;
> -	ret = btrfs_map_block(fs_info, BTRFS_MAP_READ,
> -			      bytenr, &length, &multi, mirror_num);
> -
> +	ret = __btrfs_map_block(fs_info, BTRFS_MAP_READ, bytenr, &length, &bioc,
> +				NULL, &mirror_num, 0);
>   	if (ret) {
>   		block_ctx_out->start = 0;
>   		block_ctx_out->dev_bytenr = 0;
> @@ -1478,21 +1478,26 @@ static int btrfsic_map_block(struct btrfsic_state *state, u64 bytenr, u32 len,
>   		return ret;
>   	}
>
> -	device = multi->stripes[0].dev;
> +	if (bioc)
> +		map = &bioc->stripes[0];
> +	else
> +		map = &smap;
> +
> +	device = map->dev;
>   	if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state) ||
>   	    !device->bdev || !device->name)
>   		block_ctx_out->dev = NULL;
>   	else
>   		block_ctx_out->dev = btrfsic_dev_state_lookup(
>   							device->bdev->bd_dev);
> -	block_ctx_out->dev_bytenr = multi->stripes[0].physical;
> +	block_ctx_out->dev_bytenr = map->physical;
>   	block_ctx_out->start = bytenr;
>   	block_ctx_out->len = len;
>   	block_ctx_out->datav = NULL;
>   	block_ctx_out->pagev = NULL;
>   	block_ctx_out->mem_to_free = NULL;
>
> -	kfree(multi);
> +	kfree(bioc);
>   	if (NULL == block_ctx_out->dev) {
>   		ret = -ENXIO;
>   		pr_info("btrfsic: error, cannot lookup dev (#1)!\n");