On Thu, Jun 13, 2019 at 11:43:07AM +0200, Christoph Hellwig wrote: > ->mapping isn't even used by HMM users, and the field at the same offset > in the zone_device part of the union is declared as pad. (Which btw is > rather confusing, as DAX uses ->pgmap and ->mapping from two different > sides of the union, but DAX doesn't use hmm_devmem_free). > > Signed-off-by: Christoph Hellwig <hch@xxxxxx> > --- > mm/hmm.c | 2 -- > 1 file changed, 2 deletions(-) Hurm, is hmm following this comment from mm_types.h? * If you allocate the page using alloc_pages(), you can use some of the * space in struct page for your own purposes. The five words in the main * union are available, except for bit 0 of the first word which must be * kept clear. Many users use this word to store a pointer to an object * which is guaranteed to be aligned. If you use the same storage as * page->mapping, you must restore it to NULL before freeing the page. Maybe the assumption was that a driver is using ->mapping ? However, nouveau is the only driver that uses this path, and it never touches page->mapping either (nor in -next). It looks like if a driver were to start using mapping then the driver should be responsible to set it back to NULL before being done with the page. Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx> Jason
