RE: [f2fs-dev] [PATCH V2] f2fs: check all ones or zeros bitmap withbitops for better mount performance

[Chao Yu]

Hi Lee,

> -----Original Message-----
> From: ììë [mailto:cm224.lee@xxxxxxxxxxx]
> Sent: Monday, October 28, 2013 10:20 AM
> To: 'Chao Yu'; jaegeuk.kim@xxxxxxxxxxx
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx; 'èå'; linux-kernel@xxxxxxxxxxxxxxx;
> linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> Subject: RE: [f2fs-dev] [PATCH V2] f2fs: check all ones or zeros bitmap with
> bitops for better mount performance
> 
> 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.

With the result of my test, find_next_bit takes less time than memcmp.
If we could use {test, set, clear}_bit_le intead of f2fs_{test, set, clear}_bit, the following patch
could be used for better performance.
This one is better than the V2 patch for performance with mixed bitmap in my test.

diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 7f94d78..32153eb
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -544,7 +544,8 @@ static inline void check_block_count(struct f2fs_sb_info *sbi,
        struct f2fs_sm_info *sm_info = SM_I(sbi);
        unsigned int end_segno = sm_info->segment_count - 1;
        int valid_blocks = 0;
-       int i;
+       int i, cur_pos = 0, next_pos;
+       bool is_valid;
 
        /* check segment usage */
        BUG_ON(GET_SIT_VBLOCKS(raw_sit) > sbi->blocks_per_seg);
@@ -553,9 +554,21 @@ static inline void check_block_count(struct f2fs_sb_info *sbi,
        BUG_ON(segno > end_segno);
 
        /* check bitmap with valid block count */
-       for (i = 0; i < sbi->blocks_per_seg; i++)
-               if (f2fs_test_bit(i, raw_sit->valid_map))
-                       valid_blocks++;
+       cur_pos = 0;
+       is_valid = test_bit_le(0, raw_sit->valid_map) ? true : false;
+       do {
+               if (is_valid) {
+                       next_pos = find_next_zero_bit_le(&raw_sit->valid_map,
+                                       sbi->blocks_per_seg,
+                                       cur_pos);
+                       valid_blocks += next_pos - cur_pos;
+               } else
+                       next_pos = find_next_bit_le(&raw_sit->valid_map,
+                                       sbi->blocks_per_seg,
+                                       cur_pos);
+               cur_pos = next_pos;
+               is_valid = !is_valid;
+       } while (cur_pos < sbi->blocks_per_seg);
        BUG_ON(GET_SIT_VBLOCKS(raw_sit) != valid_blocks);
 }
> 
> 
> -----Original Message-----
> From: Chao Yu [mailto:chao2.yu@xxxxxxxxxxx]
> Sent: Thursday, October 24, 2013 5:21 PM
> To: jaegeuk.kim@xxxxxxxxxxx
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx; 'èå'; linux-kernel@xxxxxxxxxxxxxxx;
> linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> 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@xxxxxxxxxxx>
> Signed-off-by: Tan Shu <shu.tan@xxxxxxxxxxx>
> Signed-off-by: Yu Chao <chao2.yu@xxxxxxxxxxx>
> ---
>  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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