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

[이창만 <cm224.lee@samsung.com>]

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.


-----Original Message-----
From: Chao Yu [mailto:chao2.yu@samsung.com] 
Sent: Thursday, October 24, 2013 5:21 PM
To: jaegeuk.kim@samsung.com
Cc: linux-fsdevel@vger.kernel.org; '谭姝'; linux-kernel@vger.kernel.org; linux-f2fs-devel@lists.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@samsung.com>
Signed-off-by: Tan Shu <shu.tan@samsung.com>
Signed-off-by: Yu Chao <chao2.yu@samsung.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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