linux-kernel - Re: [PATCH v2 07/24] ext4: support large block size in ext4_calculate

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Message-ID: <e7yz7a2l4v55ppatbhlezg4wrrvhmlqwbvkm7xctajuzmxd7mj@vmcfscarjnbf>
Date: Mon, 10 Nov 2025 10:36:56 +0100
From: Jan Kara <jack@...e.cz>
To: libaokun@...weicloud.com
Cc: linux-ext4@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca, 
	jack@...e.cz, linux-kernel@...r.kernel.org, kernel@...kajraghav.com, 
	mcgrof@...nel.org, ebiggers@...nel.org, willy@...radead.org, yi.zhang@...wei.com, 
	yangerkun@...wei.com, chengzhihao1@...wei.com, libaokun1@...wei.com
Subject: Re: [PATCH v2 07/24] ext4: support large block size in
 ext4_calculate_overhead()

On Fri 07-11-25 22:42:32, libaokun@...weicloud.com wrote:
> From: Baokun Li <libaokun1@...wei.com>
> 
> ext4_calculate_overhead() used a single page for its bitmap buffer, which
> worked fine when PAGE_SIZE >= block size. However, with block size greater
> than page size (BS > PS) support, the bitmap can exceed a single page.
> 
> To address this, we now use kvmalloc() to allocate memory of the filesystem
> block size, to properly support BS > PS.
> 
> Suggested-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Baokun Li <libaokun1@...wei.com>
> Reviewed-by: Zhang Yi <yi.zhang@...wei.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/super.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index a6314a3de51d..0d32370a459a 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -4189,7 +4189,7 @@ int ext4_calculate_overhead(struct super_block *sb)
>  	unsigned int j_blocks, j_inum = le32_to_cpu(es->s_journal_inum);
>  	ext4_group_t i, ngroups = ext4_get_groups_count(sb);
>  	ext4_fsblk_t overhead = 0;
> -	char *buf = (char *) get_zeroed_page(GFP_NOFS);
> +	char *buf = kvmalloc(sb->s_blocksize, GFP_NOFS | __GFP_ZERO);
>  
>  	if (!buf)
>  		return -ENOMEM;
> @@ -4214,7 +4214,7 @@ int ext4_calculate_overhead(struct super_block *sb)
>  		blks = count_overhead(sb, i, buf);
>  		overhead += blks;
>  		if (blks)
> -			memset(buf, 0, PAGE_SIZE);
> +			memset(buf, 0, sb->s_blocksize);
>  		cond_resched();
>  	}
>  
> @@ -4237,7 +4237,7 @@ int ext4_calculate_overhead(struct super_block *sb)
>  	}
>  	sbi->s_overhead = overhead;
>  	smp_wmb();
> -	free_page((unsigned long) buf);
> +	kvfree(buf);
>  	return 0;
>  }
>  
> -- 
> 2.46.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR