linux-ext4 - Re: LBS support for EXT4

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Message-ID: <dfad7391-e3fe-498d-8d33-55c00d8a3f46@huawei.com>
Date: Wed, 25 Jun 2025 19:51:56 +0800
From: Baokun Li <libaokun1@...wei.com>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
CC: Jan Kara <jack@...e.cz>, Luis Chamberlain <mcgrof@...nel.org>, Pankaj
 Raghav <p.raghav@...sung.com>, <linux-ext4@...r.kernel.org>, Zhang Yi
	<yi.zhang@...weicloud.com>, Theodore Ts'o <tytso@....edu>
Subject: Re: LBS support for EXT4

On 2025/6/25 19:13, Pankaj Raghav (Samsung) wrote:
> Thanks for the reply, Ted.
>
> On Mon, Jun 23, 2025 at 10:17:53AM -0400, Theodore Ts'o wrote:
>> If you want to review and test the ext4/iomap changes, that would be
>> great.  Be aware, though, that there are some features of ext4
>> (example: data journalling, fscrypt, fsverity, etc.) that the current
>> iomap buffered I/O code may not support today.  The alternatives are
>> to keep the existing ext4 code paths for those file system features,
>> or to try to add that functionality into iomap.  There are of course
>> tradeoffs to both alternatives; one might result in more code that we
>> have to maintain; the other might require a lot more work.
>>
>> It _might_ be less effort to add LBS support to native ext4 code.  I
>> think the main thing is to make sure that we always we use a large
>> folio and not fall back to a sub-blocksize set of pages.  So again,
>> it's all about tradeoffs and what you consider to be the highest
>> priority.
> @Baokun are your LBS patches based on the native ext4 code or on top of
> Zhang's iomap patches.
Now that mainline ext4 supports buffer head large folios, we'll first
focus on LBS support based on buffer heads. The main work involves adapting
ext4's internal logic (e.g., block allocation, read/write operations,
defragmentation) and clean up the process related to buffer head.

This doesn't conflict with iomap buffer write support. The iomap framework
already supports LBS (as xfs is already using it), so once ext4's internal
logic is adapted, Zhang Yi's iomap buffer write patches should also support
LBS upon their merge.


Cheers,
Baokun