On Thu, Sep 28, 2017 at 10:10:34AM +0200, Ingo Molnar wrote: > > * Kirill A. Shutemov <[email protected]> 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 <[email protected]> > > Cc: Minchan Kim <[email protected]> > > Cc: Nitin Gupta <[email protected]> > > Cc: Sergey Senozhatsky <[email protected]> > > --- > > 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. -- Kirill A. Shutemov
