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Date:   Mon, 28 Oct 2019 04:10:34 -0700
From:   Matthew Wilcox <willy@infradead.org>
To:     Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc:     linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        Michal Hocko <mhocko@suse.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>
Subject: Re: [PATCH RFC] fs/fcntl: add fcntl F_GET_RSS
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On Mon, Oct 28, 2019 at 01:28:09PM +0300, Konstantin Khlebnikov wrote:
> +	if (dax_mapping(mapping))
> +		pages = READ_ONCE(mapping->nrexceptional);
> +	else
> +		pages = READ_ONCE(mapping->nrpages);

I'm not sure this is the right calculation for DAX files.  We haven't
allocated any memory for DAX; we're just accessing storage directly.
The entries in the page caache are just translation from file offset to
physical address.