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Date: Fri, 10 Apr 2026 01:15:32 +0000
From: Jaegeuk Kim <jaegeuk@kernel.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v3] f2fs: do not support mmap write for large folio
Message-ID: <adhPNLtbAlqI8F3l@google.com>
References: <20260406154940.2407853-1-jaegeuk@kernel.org>
 <adaasm42rLxRY2GN@google.com>
 <adc7yo1_sr_eeV33@infradead.org>
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In-Reply-To: <adc7yo1_sr_eeV33@infradead.org>

On 04/08, Christoph Hellwig wrote:
> [adding back fsdevel and mm to the discussion]
> 
> On Wed, Apr 08, 2026 at 06:13:06PM +0000, Jaegeuk Kim wrote:
> > Let's check mmap writes onto the large folio, since we don't support writing
> > large folios.
> 
> What does this fix?  As state in the previous round of discussion f2fs
> only support large folios for immutable files, how do you get ->mkwrite
> called for them.

I'm approaching this as a safeguard first, since in any buggy case, this will
crash the filesystem.

> 
> The only way I can think of that is when clearing the immutable flag,
> but simply rejecting writes with SIGBUS after that seems like it's
> breaking the expected API, and I don't see handling for normal writes
> after that either.