linux-ext4 - [RFC PATCH 46/46] libext2fs: optimize ext2fs_convert_subcluster

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Date:   Wed,  8 Apr 2020 19:45:14 +0900
From:   Wang Shilong <wangshilong1991@...il.com>
To:     linux-ext4@...r.kernel.org
Cc:     lixi@....com, adilger@...ger.ca, sihara@....com,
        Li Dongyang <dongyangli@....com>
Subject: [RFC PATCH 46/46] libext2fs: optimize ext2fs_convert_subcluster_bitmap()

From: Li Dongyang <dongyangli@....com>

For a bigalloc filesystem, converting the block bitmap from blocks
to chunks in ext2fs_convert_subcluster_bitmap() can take a long time
when the device is huge, because we test the bitmap
bit-by-bit using ext2fs_test_block_bitmap2().
Use ext2fs_find_first_set_block_bitmap2() which is more efficient
for mke2fs when the fs is mostly empty.

e2fsck can also benefit from this during pass1 block scanning.

Time taken for "mke2fs -O bigalloc,extent -C 131072 -b 4096" on a 1PB
device:

without patch:
real    27m49.457s
user    21m36.474s
sys     6m9.514s

with patch:
real    6m31.908s
user    0m1.806s
sys    6m29.697s

Change-Id: I054ed3ae9e25b20de34f61358dfce3c4bd6f3092
Signed-off-by: Li Dongyang <dongyangli@....com>
Signed-off-by: Li Xi <lixi@....com>
---
 lib/ext2fs/gen_bitmap64.c | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/lib/ext2fs/gen_bitmap64.c b/lib/ext2fs/gen_bitmap64.c
index d354cffa..299fee6e 100644
--- a/lib/ext2fs/gen_bitmap64.c
+++ b/lib/ext2fs/gen_bitmap64.c
@@ -856,8 +856,7 @@ errcode_t ext2fs_convert_subcluster_bitmap(ext2_filsys fs,
 	ext2fs_generic_bitmap_64 bmap, cmap;
 	ext2fs_block_bitmap	gen_bmap = *bitmap, gen_cmap;
 	errcode_t		retval;
-	blk64_t			i, b_end, c_end;
-	int			n, ratio;
+	blk64_t			i, next, b_end, c_end;
 
 	bmap = (ext2fs_generic_bitmap_64) gen_bmap;
 	if (fs->cluster_ratio_bits == ext2fs_get_bitmap_granularity(gen_bmap))
@@ -874,18 +873,13 @@ errcode_t ext2fs_convert_subcluster_bitmap(ext2_filsys fs,
 	bmap->end = bmap->real_end;
 	c_end = cmap->end;
 	cmap->end = cmap->real_end;
-	n = 0;
-	ratio = 1 << fs->cluster_ratio_bits;
 	while (i < bmap->real_end) {
-		if (ext2fs_test_block_bitmap2(gen_bmap, i)) {
-			ext2fs_mark_block_bitmap2(gen_cmap, i);
-			i += ratio - n;
-			n = 0;
-			continue;
-		}
-		i++; n++;
-		if (n >= ratio)
-			n = 0;
+		retval = ext2fs_find_first_set_block_bitmap2(gen_bmap,
+						i, bmap->real_end, &next);
+		if (retval)
+			break;
+		ext2fs_mark_block_bitmap2(gen_cmap, next);
+		i = EXT2FS_C2B(fs, EXT2FS_B2C(fs, next) + 1);
 	}
 	bmap->end = b_end;
 	cmap->end = c_end;
-- 
2.25.2