Re: [PATCH RFC] fs/fcntl: add fcntl F_GET_RSS

[Konstantin Khlebnikov]

On 28/10/2019 14.10, Matthew Wilcox wrote:
> 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.

Yep, makes sense. If RSS declared as memory usage then this chunk must do
pages = READ_ONCE(mapping->nrpages) unconditionally and report 0 for DAX.