linux-kernel - Re: [PATCH] fs: btrfs: Optimize code execution process to save time

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20230629153331.GN16168@twin.jikos.cz>
Date:   Thu, 29 Jun 2023 17:33:31 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Lu Hongfei <luhongfei@...o.com>
Cc:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, opensource.kernel@...o.com
Subject: Re: [PATCH] fs: btrfs: Optimize code execution process to save time

On Mon, Jun 26, 2023 at 06:07:16PM +0800, Lu Hongfei wrote:
> Originally, the btrfs_check_data_free_space used round_down twice when
> aligning the range, which to some extent increased the execution time of
> the code.
> After optimization, round_down only needs to be executed once, which can
> improve code efficiency and increase code readability.

But the code is not equivalent, because there is dependency on the value
of start that changes when the line is moved.

> Signed-off-by: Lu Hongfei <luhongfei@...o.com>
> ---
>  fs/btrfs/delalloc-space.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/delalloc-space.c b/fs/btrfs/delalloc-space.c
> index 427abaf608b8..fd33b1cf1954 100644
> --- a/fs/btrfs/delalloc-space.c
> +++ b/fs/btrfs/delalloc-space.c
> @@ -137,9 +137,8 @@ int btrfs_check_data_free_space(struct btrfs_inode *inode,
>  	int ret;
>  
>  	/* align the range */
> -	len = round_up(start + len, fs_info->sectorsize) -
> -	      round_down(start, fs_info->sectorsize);

Start is used unchanged, start + len

>  	start = round_down(start, fs_info->sectorsize);
> +	len = round_up(start + len, fs_info->sectorsize) - start;

New code uses the rounded down start for round_up, then for "- start"
it's the same (that part is ok).

The changelog should explain why the code is still doing the same, not
just that it's reducing the number of round_down() calls.