linux-kernel - Re: [f2fs-dev] [PATCH V2] f2fs: check all ones or zeros bitmap with bitops for better mount performance

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Message-ID: <526DCC5C.30808@cn.fujitsu.com>
Date:	Mon, 28 Oct 2013 10:30:52 +0800
From:	Gu Zheng <guz.fnst@...fujitsu.com>
To:	이창만 <cm224.lee@...sung.com>
CC:	"'Chao Yu'" <chao2.yu@...sung.com>, jaegeuk.kim@...sung.com,
	linux-fsdevel@...r.kernel.org,
	'谭姝' <shu.tan@...sung.com>,
	linux-kernel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH V2] f2fs: check all ones or zeros bitmap with
 bitops for better mount performance

On 10/28/2013 10:19 AM, 이창만 wrote:

> To check whether bitmap are all zeros or all ones, I think memcmp is more neat.
> But I don't know exactly performance gap between memcmp and find_next_bit.

According to my understanding,
memcmp: one by one search,
find_next_bit: binary search.

Regards,
Gu

> 
> 
> -----Original Message-----
> From: Chao Yu [mailto:chao2.yu@...sung.com] 
> Sent: Thursday, October 24, 2013 5:21 PM
> To: jaegeuk.kim@...sung.com
> Cc: linux-fsdevel@...r.kernel.org; '谭姝'; linux-kernel@...r.kernel.org; linux-f2fs-devel@...ts.sourceforge.net
> Subject: [f2fs-dev] [PATCH V2] f2fs: check all ones or zeros bitmap with bitops for better mount performance
> 
> Previously, check_block_count check valid_map with bit data type in common scenario that sit has all ones or zeros bitmap, it makes low mount performance.
> So let's check the special bitmap with integer data type instead of the bit one.
> 
> v2:
>     use find_next_bit_le/find_next_zero_bit_le for better performance and readable as Jaegeuk suggested.
> 
> Suggested-by: Jaegeuk Kim <jaegeuk.kim@...sung.com>
> Signed-off-by: Tan Shu <shu.tan@...sung.com>
> Signed-off-by: Yu Chao <chao2.yu@...sung.com>
> ---
>  fs/f2fs/segment.h |   17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h index 7f94d78..d25b6af 100644
> --- a/fs/f2fs/segment.h
> +++ b/fs/f2fs/segment.h
> @@ -552,6 +552,23 @@ static inline void check_block_count(struct f2fs_sb_info *sbi,
>  	/* check boundary of a given segment number */
>  	BUG_ON(segno > end_segno);
>  
> +	/* check all ones or zeros valid_map */
> +	if (GET_SIT_VBLOCKS(raw_sit) == 0) {
> +		int pos = find_next_bit_le(&raw_sit->valid_map,
> +					sbi->blocks_per_seg,
> +					0);
> +		if (pos != sbi->blocks_per_seg)
> +			BUG();
> +		return;
> +	} else if (GET_SIT_VBLOCKS(raw_sit) == sbi->blocks_per_seg) {
> +		int pos = find_next_zero_bit_le(&raw_sit->valid_map,
> +					sbi->blocks_per_seg,
> +					0);
> +		if (pos != sbi->blocks_per_seg)
> +			BUG();
> +		return;
> +	}
> +
>  	/* check bitmap with valid block count */
>  	for (i = 0; i < sbi->blocks_per_seg; i++)
>  		if (f2fs_test_bit(i, raw_sit->valid_map))
> --
> 1.7.9.5
> 
> 
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