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List:       linux-btrfs
Subject:    Re: [PATCH 19/22] btrfs: keep track of discard reuse stats
From:       David Sterba <dsterba () suse ! cz>
Date:       2019-12-30 17:33:52
Message-ID: 20191230173352.GW3929 () twin ! jikos ! cz
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On Fri, Dec 13, 2019 at 04:22:28PM -0800, Dennis Zhou wrote:
> Keep track of how much we are discarding and how often we are reusing
> with async discard.
> 
> Signed-off-by: Dennis Zhou <dennis@kernel.org>
> Reviewed-by: Josef Bacik <josef@toxicpanda.com>
> ---
>  fs/btrfs/ctree.h            |  3 +++
>  fs/btrfs/discard.c          |  7 +++++++
>  fs/btrfs/free-space-cache.c | 14 ++++++++++++++
>  fs/btrfs/sysfs.c            | 36 ++++++++++++++++++++++++++++++++++++
>  4 files changed, 60 insertions(+)
> 
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index dddf51e27bed..edfbe6060e8d 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -474,6 +474,9 @@ struct btrfs_discard_ctl {
>  	u32 delay;
>  	u32 iops_limit;
>  	u64 bps_limit;
> +	u64 discard_extent_bytes;
> +	u64 discard_bitmap_bytes;
> +	atomic64_t discard_bytes_saved;
>  };
>  
>  /* delayed seq elem */
> diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
> index 55ad357e65f3..fe73814526ef 100644
> --- a/fs/btrfs/discard.c
> +++ b/fs/btrfs/discard.c
> @@ -419,11 +419,15 @@ static void btrfs_discard_workfn(struct work_struct *work)
>  				       block_group->discard_cursor,
>  				       btrfs_block_group_end(block_group),
>  				       minlen, maxlen, true);
> +		WRITE_ONCE(discard_ctl->discard_bitmap_bytes,
> +			   discard_ctl->discard_bitmap_bytes + trimmed);

The same argument is used for read and write, this does not seem to be a
clear usage pattern for WRITE_ONCE, is there are cleaner way to do that?

>  	} else {
>  		btrfs_trim_block_group_extents(block_group, &trimmed,
>  				       block_group->discard_cursor,
>  				       btrfs_block_group_end(block_group),
>  				       minlen, true);
> +		WRITE_ONCE(discard_ctl->discard_extent_bytes,
> +			   discard_ctl->discard_extent_bytes + trimmed);
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