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Date:   Tue, 4 Sep 2018 14:02:37 -0700
From:   Matthew Wilcox <willy@infradead.org>
To:     Vito Caputo <vcaputo@pengaru.com>
Cc:     Jeff Layton <jlayton@redhat.com>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Rogier Wolff <R.E.Wolff@BitWizard.nl>,
        =?utf-8?B?54Sm5pmT5Yas?= <milestonejxd@gmail.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: POSIX violation by writeback error
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On Tue, Sep 04, 2018 at 01:35:34PM -0700, Vito Caputo wrote:
> Implement a new class of swap space for backing dirty pages which fail
> to write back.  Pages in this space survive reboots, essentially backing
> the implicit commitment POSIX establishes in the face of asynchronous
> writeback errors.  Rather than evicting these pages as clean, they are
> swapped out to the persistent swap.

You not only need to track which index within a file this swapped page
belongs to but also which file.  And that starts to get tricky.  It may
or may not have a name; it may or may not have a persistent inode number;
it may or may not have a persistent fhandle.  If it's on network storage,
it may have been modified by another machine.  If it's on removable
storage, it may have been modified by another machine.