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Re: [PATCH] libxfs: Optimize the loop for xfs_bitmap_empty

To: Jia He <hejianet@xxxxxxxxx>
Subject: Re: [PATCH] libxfs: Optimize the loop for xfs_bitmap_empty
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Tue, 10 Nov 2015 07:54:03 -0500
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1447079482-10650-1-git-send-email-hejianet@xxxxxxxxx>
References: <1447079482-10650-1-git-send-email-hejianet@xxxxxxxxx>
User-agent: Mutt/1.5.23 (2014-03-12)
On Mon, Nov 09, 2015 at 10:31:22PM +0800, Jia He wrote:
> If there is any non zero bit in a long bitmap, it can jump out of the for 
> loop and finish the function as soon as possible.
> 
> Signed-off-by: Jia He <hejianet@xxxxxxxxx>
> Cc: Dave Chinner <david@xxxxxxxxxxxxx> 
> Cc: Brian Foster <bfoster@xxxxxxxxxx> 
> ---
>  fs/xfs/libxfs/xfs_bit.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/xfs/libxfs/xfs_bit.c b/fs/xfs/libxfs/xfs_bit.c
> index 0e8885a..84614b0 100644
> --- a/fs/xfs/libxfs/xfs_bit.c
> +++ b/fs/xfs/libxfs/xfs_bit.c
> @@ -36,6 +36,8 @@ xfs_bitmap_empty(uint *map, uint size)
>  
>       for (i = 0; i < size; i++) {
>               ret |= map[i];
> +             if (ret != 0)
> +                     return 0;
>       }
>  

Seems Ok to me, but if we're going to do this, why not just kill ret
entirely? For example, check 'if (map[i] != 0) return 0;' in the loop
and unconditionally return 1 if we make it to the end.

Brian

>       return (ret == 0);
> -- 
> 2.5.0
> 
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