On Sat 18-03-17 08:39:14, Wei Yang wrote: > The field page->flags is defined as unsigned long and is divided into > several parts to store different information of the page, like section, > node, zone. Which means all parts must sit in the one "unsigned > long". > > BITS_PER_LONG is used in several places to ensure this applies. > > #if SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > BITS_PER_LONG - NR_PAGEFLAGS > #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS > #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT+LAST_CPUPID_SHIFT <= > BITS_PER_LONG - NR_PAGEFLAGS > > While we use "sizeof(unsigned long) * 8" in the definition of > SECTIONS_PGOFF > > #define SECTIONS_PGOFF ((sizeof(unsigned long)*8) - > SECTIONS_WIDTH) > > This may not be that obvious for audience to catch the point. > > This patch replaces the "sizeof(unsigned long) * 8" with BITS_PER_LONG to > make all this consistent.
I am not really sure this is an improvement. page::flags is unsigned long nad the current code reflects that type. > Signed-off-by: Wei Yang <richard.weiy...@gmail.com> > --- > include/linux/mm.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index b84615b0f64c..a5d80de089ff 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -684,7 +684,7 @@ int finish_mkwrite_fault(struct vm_fault *vmf); > */ > > /* Page flags: | [SECTION] | [NODE] | ZONE | [LAST_CPUPID] | ... | FLAGS | */ > -#define SECTIONS_PGOFF ((sizeof(unsigned long)*8) - > SECTIONS_WIDTH) > +#define SECTIONS_PGOFF (BITS_PER_LONG - SECTIONS_WIDTH) > #define NODES_PGOFF (SECTIONS_PGOFF - NODES_WIDTH) > #define ZONES_PGOFF (NODES_PGOFF - ZONES_WIDTH) > #define LAST_CPUPID_PGOFF (ZONES_PGOFF - LAST_CPUPID_WIDTH) > -- > 2.11.0 > -- Michal Hocko SUSE Labs
