linux-ext4 - Re: [PATCH 24/25] ext4: add checks for large folio incompatibilities when BS

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Message-ID: <arj5yptdhk2tptkqu6q2kwbyhh5cx4ncfyz3hfhlfikx57yf4a@nolkehxy2kqs>
Date: Wed, 5 Nov 2025 10:59:37 +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, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, 
	yi.zhang@...wei.com, yangerkun@...wei.com, chengzhihao1@...wei.com, 
	libaokun1@...wei.com
Subject: Re: [PATCH 24/25] ext4: add checks for large folio incompatibilities
 when BS > PS

On Sat 25-10-25 11:22:20, libaokun@...weicloud.com wrote:
> From: Baokun Li <libaokun1@...wei.com>
> 
> Supporting a block size greater than the page size (BS > PS) requires
> support for large folios. However, several features (e.g., verity, encrypt)
> and mount options (e.g., data=journal) do not yet support large folios.
> 
> To prevent conflicts, this patch adds checks at mount time to prohibit
> these features and options from being used when BS > PS. Since the data
> mode cannot be changed on remount, there is no need to check on remount.
> 
> A new mount flag, EXT4_MF_LARGE_FOLIO, is introduced. This flag is set
> after the checks pass, indicating that the filesystem has no features or
> mount options incompatible with large folios. Subsequent checks can simply
> test for this flag to avoid redundant verifications.
> 
> 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/ext4.h  |  3 ++-
>  fs/ext4/inode.c | 10 ++++------
>  fs/ext4/super.c | 26 ++++++++++++++++++++++++++
>  3 files changed, 32 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 8223ed29b343..f1163deb0812 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1859,7 +1859,8 @@ static inline int ext4_get_resgid(struct ext4_super_block *es)
>  enum {
>  	EXT4_MF_MNTDIR_SAMPLED,
>  	EXT4_MF_FC_INELIGIBLE,	/* Fast commit ineligible */
> -	EXT4_MF_JOURNAL_DESTROY	/* Journal is in process of destroying */
> +	EXT4_MF_JOURNAL_DESTROY,/* Journal is in process of destroying */
> +	EXT4_MF_LARGE_FOLIO,	/* large folio is support */
>  };
>  
>  static inline void ext4_set_mount_flag(struct super_block *sb, int bit)
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index b3fa29923a1d..04f9380d4211 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5143,14 +5143,12 @@ static bool ext4_should_enable_large_folio(struct inode *inode)
>  {
>  	struct super_block *sb = inode->i_sb;
>  
> -	if (!S_ISREG(inode->i_mode))
> -		return false;
> -	if (test_opt(sb, DATA_FLAGS) == EXT4_MOUNT_JOURNAL_DATA ||
> -	    ext4_test_inode_flag(inode, EXT4_INODE_JOURNAL_DATA))
> +	if (!ext4_test_mount_flag(sb, EXT4_MF_LARGE_FOLIO))
>  		return false;
> -	if (ext4_has_feature_verity(sb))
> +
> +	if (!S_ISREG(inode->i_mode))
>  		return false;
> -	if (ext4_has_feature_encrypt(sb))
> +	if (ext4_test_inode_flag(inode, EXT4_INODE_JOURNAL_DATA))
>  		return false;
>  
>  	return true;
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 7338c708ea1d..fdc006a973aa 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -5034,6 +5034,28 @@ static const char *ext4_has_journal_option(struct super_block *sb)
>  	return NULL;
>  }
>  
> +static int ext4_check_large_folio(struct super_block *sb)
> +{
> +	const char *err_str = NULL;
> +
> +	if (test_opt(sb, DATA_FLAGS) == EXT4_MOUNT_JOURNAL_DATA)
> +		err_str = "data=journal";
> +	else if (ext4_has_feature_verity(sb))
> +		err_str = "verity";
> +	else if (ext4_has_feature_encrypt(sb))
> +		err_str = "encrypt";
> +
> +	if (!err_str) {
> +		ext4_set_mount_flag(sb, EXT4_MF_LARGE_FOLIO);
> +	} else if (sb->s_blocksize > PAGE_SIZE) {
> +		ext4_msg(sb, KERN_ERR, "bs(%lu) > ps(%lu) unsupported for %s",
> +			 sb->s_blocksize, PAGE_SIZE, err_str);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  static int ext4_load_super(struct super_block *sb, ext4_fsblk_t *lsb,
>  			   int silent)
>  {
> @@ -5310,6 +5332,10 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
>  
>  	ext4_apply_options(fc, sb);
>  
> +	err = ext4_check_large_folio(sb);
> +	if (err < 0)
> +		goto failed_mount;
> +
>  	err = ext4_encoding_init(sb, es);
>  	if (err)
>  		goto failed_mount;
> -- 
> 2.46.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR