linux-ext4 - Re: [PATCH 2/2] iomap: fall back to buffered writes for invalidation failures

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Date:   Tue, 14 Jul 2020 13:00:11 +0200
From:   Christoph Hellwig <hch@....de>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Christoph Hellwig <hch@....de>, Dave Chinner <david@...morbit.com>,
        Goldwyn Rodrigues <rgoldwyn@...e.de>,
        Damien Le Moal <damien.lemoal@....com>,
        Naohiro Aota <naohiro.aota@....com>,
        Johannes Thumshirn <jth@...nel.org>,
        linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        cluster-devel@...hat.com, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org
Subject: Re: [PATCH 2/2] iomap: fall back to buffered writes for
 invalidation failures

On Mon, Jul 13, 2020 at 12:55:09PM +0100, Matthew Wilcox wrote:
> On Mon, Jul 13, 2020 at 09:46:33AM +0200, Christoph Hellwig wrote:
> > Failing to invalid the page cache means data in incoherent, which is
> > a very bad state for the system.  Always fall back to buffered I/O
> > through the page cache if we can't invalidate mappings.
> 
> Is that the right approach though?  I don't have a full picture in my head,
> but wouldn't we be better off marking these pages as !Uptodate and doing
> the direct I/O?

Isn't that a problem if e.g. pages are mapped into userspace and mlocked?