Re: [PATCH 2/6] e2fsck: optimize pass1 for CPU time

["Lukáš Czerner" <lczerner@redhat.com>]

On Sat, 24 Nov 2012, Theodore Ts'o wrote:

> Date: Sat, 24 Nov 2012 19:36:30 -0500
> From: Theodore Ts'o <tytso@mit.edu>
> To: Ext4 Developers List <linux-ext4@vger.kernel.org>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Subject: [PATCH 2/6] e2fsck: optimize pass1 for CPU time
> 
> Optimize e2fsck pass 1 by marking entire extents as being in use at a
> time, instead of block by block.  This optimization only works for
> non-bigalloc file systems for now (it's tricky to handle bigalloc file
> systems since this code is also responsible for dealing with blocks
> that are not correctly aligned within a cluster).  When the
> optimization works, the CPU savings can be significant: up to two or
> three CPU minutes for a full 4T disk.
> 
> Addresses-Google-Bug: #7534813

Looks good.

Reviewed-by: Lukas Czerner <lczerner@redhat.com>

> 
> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
> ---
>  e2fsck/pass1.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/e2fsck/pass1.c b/e2fsck/pass1.c
> index 78fbe8d..cc00e0f 100644
> --- a/e2fsck/pass1.c
> +++ b/e2fsck/pass1.c
> @@ -1432,6 +1432,16 @@ static _INLINE_ void mark_block_used(e2fsck_t ctx, blk64_t block)
>  	}
>  }
>  
> +static _INLINE_ void mark_blocks_used(e2fsck_t ctx, blk64_t block,
> +				      unsigned int num)
> +{
> +	if (ext2fs_test_block_bitmap_range2(ctx->block_found_map, block, num))
> +		ext2fs_mark_block_bitmap_range2(ctx->block_found_map, block, num);
> +	else
> +		while (num--)
> +			mark_block_used(ctx, block++);
> +}
> +
>  /*
>   * Adjust the extended attribute block's reference counts at the end
>   * of pass 1, either by subtracting out references for EA blocks that
> @@ -1867,11 +1877,15 @@ static void scan_extent_node(e2fsck_t ctx, struct problem_context *pctx,
>  				goto failed_add_dir_block;
>  			}
>  		}
> +		if (!ctx->fs->cluster_ratio_bits) {
> +			mark_blocks_used(ctx, extent.e_pblk, extent.e_len);
> +			pb->num_blocks += extent.e_len;
> +		}
>  		for (blk = extent.e_pblk, blockcnt = extent.e_lblk, i = 0;
>  		     i < extent.e_len;
>  		     blk++, blockcnt++, i++) {
> -			if (!(ctx->fs->cluster_ratio_bits &&
> -			      pb->previous_block &&
> +			if (ctx->fs->cluster_ratio_bits &&
> +			    !(pb->previous_block &&
>  			      (EXT2FS_B2C(ctx->fs, blk) ==
>  			       EXT2FS_B2C(ctx->fs, pb->previous_block)) &&
>  			      (blk & EXT2FS_CLUSTER_MASK(ctx->fs)) ==
>