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

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Message-ID: <20251110043226.GD2988753@mit.edu>
Date: Sun, 9 Nov 2025 23:32:26 -0500
From: "Theodore Ts'o" <tytso@....edu>
To: libaokun@...weicloud.com
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
Subject: Re: [PATCH v2 00/24] ext4: enable block size larger than page size

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.

					- Ted