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Date: Mon, 30 Jun 2025 07:45:42 +0200
From: Christoph Hellwig <hch@lst.de>
To: Brian Foster <bfoster@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>, Christian Brauner <brauner@kernel.org>,
	"Darrick J. Wong" <djwong@kernel.org>,
	Joanne Koong <joannelkoong@gmail.com>, linux-xfs@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-block@vger.kernel.org, gfs2@lists.linux.dev
Subject: Re: [PATCH 08/12] iomap: move folio_unlock out of
 iomap_writeback_folio
Message-ID: <20250630054542.GE28532@lst.de>
References: <20250627070328.975394-1-hch@lst.de> <20250627070328.975394-9-hch@lst.de> <aF7JHFdLCi89sFpn@bfoster>
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In-Reply-To: <aF7JHFdLCi89sFpn@bfoster>
User-Agent: Mutt/1.5.17 (2007-11-01)

On Fri, Jun 27, 2025 at 12:38:52PM -0400, Brian Foster wrote:
> > Move unlocking the folio out of iomap_writeback_folio into the caller.
> > This means the end writeback machinery is now run with the folio locked
> > when no writeback happend, or writeback completed extremely fast.
> > 
> 
> I notice that folio_end_dropbehind_write() (via folio_end_writeback())
> wants to trylock the folio in order to do its thing. Is this going to
> cause issues with that (i.e. prevent invalidations)?

Good point.  It renders the filemap_end_dropbehind_write call (the
function got renamed in 6.16-rc) essentially useless.  OTOH this is
the case where no writeback happened due to a race, so it isn't needed
to start with.  But it might be worth documenting that fact.