linux-ext4 - Re: [PATCH 07/25] ext4: support large block size in ext4_calculate

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Message-ID: <70fd2f0e-8fac-4be7-9597-7072a36a58bc@huawei.com>
Date: Mon, 3 Nov 2025 22:37:45 +0800
From: Baokun Li <libaokun1@...wei.com>
To: Jan Kara <jack@...e.cz>
CC: <linux-ext4@...r.kernel.org>, <tytso@....edu>, <adilger.kernel@...ger.ca>,
	<linux-kernel@...r.kernel.org>, <kernel@...kajraghav.com>,
	<mcgrof@...nel.org>, <linux-fsdevel@...r.kernel.org>, <linux-mm@...ck.org>,
	<yi.zhang@...wei.com>, <yangerkun@...wei.com>, <chengzhihao1@...wei.com>,
	<libaokun1@...wei.com>, Baokun Li <libaokun@...weicloud.com>
Subject: Re: [PATCH 07/25] ext4: support large block size in
 ext4_calculate_overhead()

On 2025-11-03 16:14, Jan Kara wrote:
> On Sat 25-10-25 11:22:03, 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 __get_free_pages() to allocate multiple pages,
>> sized to the block size, to properly support BS > PS.
>>
>> Signed-off-by: Baokun Li <libaokun1@...wei.com>
>> Reviewed-by: Zhang Yi <yi.zhang@...wei.com>
> One comment below:
>
>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>> index d353e25a5b92..7338c708ea1d 100644
>> --- a/fs/ext4/super.c
>> +++ b/fs/ext4/super.c
>> @@ -4182,7 +4182,8 @@ 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);
>> +	gfp_t gfp = GFP_NOFS | __GFP_ZERO;
>> +	char *buf = (char *)__get_free_pages(gfp, sbi->s_min_folio_order);
> I think this should be using kvmalloc(). There's no reason to require
> physically contiguous pages for this...
>
> 								Honza

Makes sense, I will use kvmalloc() in the next version.


Thanks,
Baokun