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Date: Wed, 26 Aug 2026 09:42:15 +0200
From: Christoph Hellwig <hch@lst.de>
To: Matthew Wilcox <willy@infradead.org>
Cc: Jann Horn <jannh@google.com>, Pedro Falcato <pfalcato@suse.de>,
	Christoph Hellwig <hch@lst.de>, David Howells <dhowells@redhat.com>,
	John Hubbard <jhubbard@nvidia.com>, Jan Kara <jack@suse.cz>,
	Rik van Riel <riel@surriel.com>, Qu Wenruo <wqu@suse.com>,
	"Darrick J. Wong" <djwong@kernel.org>, linux-btrfs@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-xfs@vger.kernel.org, linux-rdma@vger.kernel.org,
	Leon Romanovsky <leon@kernel.org>, Jason Gunthorpe <jgg@nvidia.com>
Subject: Re: Removing ->dirty_folio
Message-ID: <20260826074215.GA18668@lst.de>
References: <aoyWln-Gt-yvZQkE@casper.infradead.org> <CAG48ez0vXVUu9j4rYUeCqgwyHKAiN_6fL--D90WvX9q7B41V-A@mail.gmail.com> <ao3y8TtEGjniZ_4f@casper.infradead.org> <20260826050733.GB15122@lst.de>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Wed, Aug 26, 2026 at 07:07:33AM +0200, Christoph Hellwig wrote:
> The interesting case is FOLL_LONGTERM, as it can pin I/O for a much
> longer time.  And that also means IFF the user of FOLL_LONGTERM actually
> wants to be able to persist data on a shared mmap, it has to manually
> dirty folios one or more times during the FOLL_LONGTERM pin, because
> otherwise the file system would never know there is dirty data.
> The set_page_dirty call in ib_umem_odp_unmap_dma_pages is an example
> for that.

... not to forget the epic boss of this genre: vmsplice, which is also
still using get_user_pages_fast/FOLL_GET through iov_iter_get_pages2.