linux-kernel - Re: [PATCH v2 00/24] ext4: enable block size larger than page size

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Message-ID: <6d6945a4-6672-45d1-a7fc-0736df452895@huawei.com>
Date: Mon, 10 Nov 2025 14:18:41 +0800
From: Baokun Li <libaokun1@...wei.com>
To: Theodore Ts'o <tytso@....edu>
CC: <linux-ext4@...r.kernel.org>, <adilger.kernel@...ger.ca>, <jack@...e.cz>,
	<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>,
	<libaokun1@...wei.com>, Baokun Li <libaokun@...weicloud.com>
Subject: Re: [PATCH v2 00/24] ext4: enable block size larger than page size

On 2025-11-10 12:32, Theodore Ts'o wrote:
> I've started looking at this patch series and playing with it, and one
> thing which is worth noting is that CONFIG_TRANSPARENT_HUGEPAGE needs
> to be enabled, or else sb_set_blocksize() will fail for block size >
> page size.  This isn't specific to ext4, and maybe I'm missing
> something, but apparently this isn't documented.  I had to go digging
> through the source code to figure out what was needed.
>
> I wonder if we should have some kind of warning in sb_set_blocksize()
> where if there is an attempt to set a blocksize > page size and
> transparent hugepages is not configured, we issue a printk_once()
> giving a hint to the user that the reason that the mount failed was
> because transparent hugepages wasn't enabled at compile time.
>
> It **really** isn't obvious that large block size support and
> transparent hugepages are linked.
>
Thank you for the review!

Yes, supporting block sizes larger than the page size requires large
folios, so it is indeed necessary to enable CONFIG_TRANSPARENT_HUGEPAGE
to support large folios. Because the code is wrapped in multiple layers,
the connection between the two is somewhat hidden, and users may not
notice it or know how to enable LBS.

I will add some hints in sb_set_blocksize to make users aware of this
relationship. Thanks for the suggestion!


Cheers,
Baokun