On Mon, 2019-09-09 at 12:56 +0300, Kirill A. Shutemov wrote: > On Sat, Sep 07, 2019 at 10:25:28AM -0700, Alexander Duyck wrote: > > From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> > > > > In order to support page reporting it will be necessary to store and > > retrieve the migratetype of a page. To enable that I am moving the set and > > get operations for pcppage_migratetype into the mm/internal.h header so > > that they can be used outside of the page_alloc.c file. > > > > Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx> > > Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> > > I'm not sure that it's great idea to export this functionality beyond > mm/page_alloc.c without any additional safeguards. How would we avoid to > messing with ->index when the page is not in the right state of its > life-cycle. Can we add some VM_BUG_ON()s here? I am not sure what we would need to check on though. There are essentially 2 cases where we are using this. The first is the percpu page lists so the value is set either as a result of __rmqueue_smallest or free_unref_page_prepare. The second one which hasn't been added yet is for the Reported pages case which I add with patch 6. When I use it for page reporting I am essentially using the Reported flag to identify what pages in the buddy list will have this value set versus those that may not. I didn't explicitly define it that way, but that is how I am using it so that the value cannot be trusted unless the Reported flag is set.
