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From:   Andreas Dilger <adilger@dilger.ca>
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Subject: Re: [PATCH v2 1/4] libext2fs: optimize
 ext2fs_convert_subcluster_bitmap()
Date:   Sun, 25 Aug 2019 21:14:42 -0600
In-Reply-To: <20190822082617.19180-1-dongyangli@ddn.com>
Cc:     "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>
To:     Dongyang Li <dongyangli@ddn.com>
References: <20190822082617.19180-1-dongyangli@ddn.com>
Sender: linux-ext4-owner@vger.kernel.org
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On Aug 22, 2019, at 2:26 AM, Dongyang Li <dongyangli@ddn.com> wrote:
>=20
> 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.
>=20
> e2fsck can also benefit from this during pass1 block scanning.
>=20
> Time taken for "mke2fs -O bigalloc,extent -C 131072 -b 4096" on a 1PB
> device:
>=20
> without patch:
> real    27m49.457s
> user    21m36.474s
> sys     6m9.514s
>=20
> with patch:
> real    6m31.908s
> user    0m1.806s
> sys    6m29.697s
>=20
> Signed-off-by: Li Dongyang <dongyangli@ddn.com>

Reviewed-by: Andreas Dilger <adilger@dilger.ca>

> ---
> lib/ext2fs/gen_bitmap64.c | 20 +++++++-------------
> 1 file changed, 7 insertions(+), 13 deletions(-)
>=20
> diff --git a/lib/ext2fs/gen_bitmap64.c b/lib/ext2fs/gen_bitmap64.c
> index 6e4d8b71..f1dd1891 100644
> --- a/lib/ext2fs/gen_bitmap64.c
> +++ b/lib/ext2fs/gen_bitmap64.c
> @@ -799,8 +799,7 @@ errcode_t =
ext2fs_convert_subcluster_bitmap(ext2_filsys fs,
> 	ext2fs_generic_bitmap_64 bmap, cmap;
> 	ext2fs_block_bitmap	gen_bmap =3D *bitmap, gen_cmap;
> 	errcode_t		retval;
> -	blk64_t			i, b_end, c_end;
> -	int			n, ratio;
> +	blk64_t			i, next, b_end, c_end;
>=20
> 	bmap =3D (ext2fs_generic_bitmap_64) gen_bmap;
> 	if (fs->cluster_ratio_bits =3D=3D =
ext2fs_get_bitmap_granularity(gen_bmap))
> @@ -817,18 +816,13 @@ errcode_t =
ext2fs_convert_subcluster_bitmap(ext2_filsys fs,
> 	bmap->end =3D bmap->real_end;
> 	c_end =3D cmap->end;
> 	cmap->end =3D cmap->real_end;
> -	n =3D 0;
> -	ratio =3D 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 +=3D ratio - n;
> -			n =3D 0;
> -			continue;
> -		}
> -		i++; n++;
> -		if (n >=3D ratio)
> -			n =3D 0;
> +		retval =3D ext2fs_find_first_set_block_bitmap2(gen_bmap,
> +						i, bmap->real_end, =
&next);
> +		if (retval)
> +			break;
> +		ext2fs_mark_block_bitmap2(gen_cmap, next);
> +		i =3D EXT2FS_C2B(fs, EXT2FS_B2C(fs, next) + 1);
> 	}
> 	bmap->end =3D b_end;
> 	cmap->end =3D c_end;
> --
> 2.22.1
>=20


Cheers, Andreas


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