[v1] ext4: enable block size larger than page size

[PATCH 07/25] ext4: support large block size in ext4_calculate_overhead()

Posted by libaokun@huaweicloud.com 3 months, 2 weeks ago

From: Baokun Li <libaokun1@huawei.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@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
---
 fs/ext4/super.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

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);
 
 	if (!buf)
 		return -ENOMEM;
@@ -4207,7 +4208,7 @@ 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();
 	}
 
@@ -4230,7 +4231,7 @@ int ext4_calculate_overhead(struct super_block *sb)
 	}
 	sbi->s_overhead = overhead;
 	smp_wmb();
-	free_page((unsigned long) buf);
+	free_pages((unsigned long)buf, sbi->s_min_folio_order);
 	return 0;
 }
 
-- 
2.46.1

Re: [PATCH 07/25] ext4: support large block size in ext4_calculate_overhead()

Posted by Jan Kara 3 months, 1 week ago

On Sat 25-10-25 11:22:03, libaokun@huaweicloud.com wrote:
> From: Baokun Li <libaokun1@huawei.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@huawei.com>
> Reviewed-by: Zhang Yi <yi.zhang@huawei.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
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH 07/25] ext4: support large block size in ext4_calculate_overhead()

Posted by Baokun Li 3 months, 1 week ago

On 2025-11-03 16:14, Jan Kara wrote:
> On Sat 25-10-25 11:22:03, libaokun@huaweicloud.com wrote:
>> From: Baokun Li <libaokun1@huawei.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@huawei.com>
>> Reviewed-by: Zhang Yi <yi.zhang@huawei.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