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	Thu, 28 May 2026 12:49:40 +0000
Date: Thu, 28 May 2026 05:49:40 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: Tal Zussman <tz2294@columbia.edu>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Hildenbrand <david@kernel.org>,
	Lorenzo Stoakes <ljs@kernel.org>,
	"Liam R. Howlett" <liam@infradead.org>,
	Vlastimil Babka <vbabka@kernel.org>,
	Mike Rapoport <rppt@kernel.org>,
	Suren Baghdasaryan <surenb@google.com>,
	Michal Hocko <mhocko@suse.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christian Brauner <brauner@kernel.org>,
	Jens Axboe <axboe@kernel.dk>, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	io-uring@vger.kernel.org
Subject: Re: [PATCH RFC 00/11] mm/filemap: split out folio wait and VFS code
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References: <20260520-filemap-split-v1-0-c36ddc2b6cf2@columbia.edu>
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On Thu, May 28, 2026 at 11:22:37AM +0200, Jan Kara wrote:
> Overall this makes sense to me. In particular I agree it makes sense to
> move the file read/write helpers into fs.

I disagree very strongly.  Mixing default implementations with the
higher level APIs is a really bad idea and leads to people taking
stupid shortcuts and other layering violations.

Splitting up filemap.c makes sense, but I'd rather keep the generic copy
into and out of the pagecache code with the MM infrastructure for it,
as it is not VFS code, and making that clear to anyone touching the code
is important.