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Date:   Tue, 14 Sep 2021 16:09:02 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 3/3] resize2fs: optimize
 resize2fs_calculate_summary_stats()

On Tue, Sep 14, 2021 at 03:11:04PM -0400, Theodore Ts'o wrote:
> Speed up an off-line resize of a 10GB file system to 64TB located on
> tmpfs from 90 seconds to 16 seconds by extracting block group bitmaps
> using a population count function to count the blocks in use instead
> checking each bit in the block bitmap.
> 
> Signed-off-by: Theodore Ts'o <tytso@....edu>
> ---
>  resize/resize2fs.c | 74 ++++++++++++++--------------------------------
>  1 file changed, 23 insertions(+), 51 deletions(-)
> 
> diff --git a/resize/resize2fs.c b/resize/resize2fs.c
> +		retval = ext2fs_get_block_bitmap_range2(fs->block_map,
> +			C2B(blk), fs->super->s_clusters_per_group, bitmap_buf);

Whoops, this should be B2C to convert a block number to a cluster
number.

Hmm, I note that this wasn't picked up by our regression tests.
Mental note to self --- we need to add more regression tests to better
exercise bigalloc resizes.  Currently we have a big warning which gets
printed about off-line resizes of bigalloc file systems being
experimentlal, but we should aim to do better.  :-)

	       	      	     	    - Ted

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