linux-kernel - Re: [PATCH v2 21/24] ext4: make data=journal support large block size

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Message-ID: <5be37f62-500f-42cb-838b-e017a5c227fd@huawei.com>
Date: Mon, 10 Nov 2025 19:53:41 +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>, <ebiggers@...nel.org>, <willy@...radead.org>,
	<yi.zhang@...wei.com>, <yangerkun@...wei.com>, <chengzhihao1@...wei.com>,
	<libaokun@...weicloud.com>
Subject: Re: [PATCH v2 21/24] ext4: make data=journal support large block size

On 2025-11-10 17:48, Jan Kara wrote:
> On Fri 07-11-25 22:42:46, libaokun@...weicloud.com wrote:
>> From: Baokun Li <libaokun1@...wei.com>
>>
>> Currently, ext4_set_inode_mapping_order() does not set max folio order
>> for files with the data journalling flag. For files that already have
>> large folios enabled, ext4_inode_journal_mode() ignores the data
>> journalling flag once max folio order is set.
>>
>> This is not because data journalling cannot work with large folios, but
>> because credit estimates will go through the roof if there are too many
>> blocks per folio.
>>
>> Since the real constraint is blocks-per-folio, to support data=journal
>> under LBS, we now set max folio order to be equal to min folio order for
>> files with the journalling flag. When LBS is disabled, the max folio order
>> remains unset as before.
>>
>> Additionally, the max_order check in ext4_inode_journal_mode() is removed,
>> and mapping order is reset in ext4_change_inode_journal_flag().
>>
>> Suggested-by: Jan Kara <jack@...e.cz>
>> Signed-off-by: Baokun Li <libaokun1@...wei.com>
> ...
>
>> @@ -6585,6 +6590,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
>>  		ext4_clear_inode_flag(inode, EXT4_INODE_JOURNAL_DATA);
>>  	}
>>  	ext4_set_aops(inode);
>> +	ext4_set_inode_mapping_order(inode);
>>  
>>  	jbd2_journal_unlock_updates(journal);
>>  	ext4_writepages_up_write(inode->i_sb, alloc_ctx);
> I think more needs to be done here because this way we could leave folios
> in the page cache that would be now larger than max order. To simplify the
> logic I'd make filemap_write_and_wait() call in
> ext4_change_inode_journal_flag() unconditional and add there
> truncate_pagecache() call to evict all the page cache before we switch the
> inode journalling mode.
>
> 								Honza

That makes sense. I forgot to truncate the old page cache here.

I will make the changes according to your suggestion in the next version.

Thank you for your advice!


Cheers,
Baokun