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

From: Konstantin Khlebnikov
Date: Mon Oct 28 2019 - 07:21:00 EST

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.