Re: [PATCH] mm: use BITS_PER_LONG to unify the definition in page->flags
On Sun, Mar 19, 2017 at 11:08:22AM -0400, Michal Hocko wrote: >On Sun 19-03-17 23:03:45, Wei Yang wrote: >> On Sun, Mar 19, 2017 at 10:30:13AM -0400, Michal Hocko wrote: >> >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. >> > >> >> Hi, Michal >> >> Glad to hear from you. >> >> I think the purpose of definition BITS_PER_LONG is more easily to let >> audience >> know it is the number of bits of type long. If it has no improvement, we >> don't >> need to define a specific macro . >> >> And as you could see, several related macros use BITS_PER_LONG in their >> definition. After this change, all of them will have a consistent definition. >> >> After this change, code looks more neat :-) >> >> So it looks more reasonable to use this. > >I do not think that this is sufficient to justify the change. > Fine~ Thanks for comments~ >-- >Michal Hocko >SUSE Labs -- Wei Yang Help you, Help me signature.asc Description: PGP signature
Re: [PATCH] mm: use BITS_PER_LONG to unify the definition in page->flags
On Sun 19-03-17 23:03:45, Wei Yang wrote: > On Sun, Mar 19, 2017 at 10:30:13AM -0400, Michal Hocko wrote: > >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. > > > > Hi, Michal > > Glad to hear from you. > > I think the purpose of definition BITS_PER_LONG is more easily to let audience > know it is the number of bits of type long. If it has no improvement, we don't > need to define a specific macro . > > And as you could see, several related macros use BITS_PER_LONG in their > definition. After this change, all of them will have a consistent definition. > > After this change, code looks more neat :-) > > So it looks more reasonable to use this. I do not think that this is sufficient to justify the change. -- Michal Hocko SUSE Labs
Re: [PATCH] mm: use BITS_PER_LONG to unify the definition in page->flags
On Sun, Mar 19, 2017 at 10:30:13AM -0400, Michal Hocko wrote: >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. > Hi, Michal Glad to hear from you. I think the purpose of definition BITS_PER_LONG is more easily to let audience know it is the number of bits of type long. If it has no improvement, we don't need to define a specific macro . And as you could see, several related macros use BITS_PER_LONG in their definition. After this change, all of them will have a consistent definition. After this change, code looks more neat :-) So it looks more reasonable to use this. -- Wei Yang Help you, Help me signature.asc Description: PGP signature
Re: [PATCH] mm: use BITS_PER_LONG to unify the definition in page->flags
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 > --- > 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
