On Mon, 2019-09-09 at 11:01 -0700, Alexander Duyck wrote: > 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. I guess the alternative would be to just treat the ->index value as the index within the boundary array, and not use the per-cpu list functions. Doing that might make things a bit more clear since all we are really doing is storing the index into the boundary list the page is contained in. I could probably combine the value of order and migratetype and save myself a few cycles in the process by just saving the index into the array directly.
