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
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