* Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > On Thu, Sep 28, 2017 at 10:10:34AM +0200, Ingo Molnar wrote: > > > > * Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > > > > > With boot-time switching between paging mode we will have variable > > > MAX_PHYSMEM_BITS. > > > > > > Let's use the maximum variable possible for CONFIG_X86_5LEVEL=y > > > configuration to define zsmalloc data structures. > > > > > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > > > Cc: Minchan Kim <minchan@xxxxxxxxxx> > > > Cc: Nitin Gupta <ngupta@xxxxxxxxxx> > > > Cc: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx> > > > --- > > > mm/zsmalloc.c | 6 ++++++ > > > 1 file changed, 6 insertions(+) > > > > > > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c > > > index 7c38e850a8fc..fe22661f2fe5 100644 > > > --- a/mm/zsmalloc.c > > > +++ b/mm/zsmalloc.c > > > @@ -93,7 +93,13 @@ > > > #define MAX_PHYSMEM_BITS BITS_PER_LONG > > > #endif > > > #endif > > > + > > > +#ifdef CONFIG_X86_5LEVEL > > > +/* MAX_PHYSMEM_BITS is variable, use maximum value here */ > > > +#define _PFN_BITS (52 - PAGE_SHIFT) > > > +#else > > > #define _PFN_BITS (MAX_PHYSMEM_BITS - PAGE_SHIFT) > > > +#endif > > > > This is a totally ugly hack, polluting generic MM code with an x86-ism and an > > arbitrary hard-coded constant that would silently lose validity when x86 paging > > gets extended again ... > > Well, yes it's ugly. And I would be glad to find better solution. But I > don't see one. > > And it won't break silently on x86 paging expanding as it won't use > CONFIG_X86_5LEVEL, so we would fallback to MAX_PHYSMEM_BITS - PAGE_SHIFT. > > I worth noting that the code already has x86 hack. See PAE special case > for MAX_PHYSMEM_BITS. Old mistakes don't justify new ones. It's possible to do better: for example if we provide a MAX_POSSIBLE_PHYSMEM_BITS define that is the higher value then code which needs this for sizing can use it? That could eliminate the PAE dependency as well perhaps. Thanks, Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
