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Groups > linux.kernel > #1604020
| From | Wei Yang <richard.weiyang@gmail.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH] mm: use BITS_PER_LONG to unify the definition in page->flags |
| Date | 2017-03-19 17:10 +0100 |
| Message-ID | <tmLz4-89I-1@gated-at.bofh.it> (permalink) |
| References | <tmaJb-6zz-1@gated-at.bofh.it> <tmKjD-75i-1@gated-at.bofh.it> <tmKCZ-7uc-9@gated-at.bofh.it> <tmKCZ-7uc-7@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
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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
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[PATCH] mm: use BITS_PER_LONG to unify the definition in page->flags Wei Yang <richard.weiyang@gmail.com> - 2017-03-18 01:50 +0100
Re: [PATCH] mm: use BITS_PER_LONG to unify the definition in page->flags Michal Hocko <mhocko@kernel.org> - 2017-03-19 15:50 +0100
Re: [PATCH] mm: use BITS_PER_LONG to unify the definition in page->flags Michal Hocko <mhocko@kernel.org> - 2017-03-19 16:10 +0100
Re: [PATCH] mm: use BITS_PER_LONG to unify the definition in page->flags Wei Yang <richard.weiyang@gmail.com> - 2017-03-19 17:10 +0100
Re: [PATCH] mm: use BITS_PER_LONG to unify the definition in page->flags Wei Yang <richard.weiyang@gmail.com> - 2017-03-19 16:10 +0100
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