Messages in this thread | | | Date | Wed, 22 Oct 2008 22:30:55 +0400 | From | Cyrill Gorcunov <> | Subject | Re: [RFC] SLUB - define OO_ macro instead of hardcoded numbers |
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[Christoph Lameter - Wed, Oct 22, 2008 at 11:24:58AM -0700] > On Wed, 22 Oct 2008, Cyrill Gorcunov wrote: > >> [Christoph Lameter - Wed, Oct 22, 2008 at 11:10:56AM -0700] >>> On Wed, 22 Oct 2008, Cyrill Gorcunov wrote: >>> >>>> +#define OO_SHIFT 16 >>>> +#define OO_MASK ((1 << OO_SHIFT) - 1) >>>> +#define MAX_OBJS_PER_PAGE 65535 /* see struct page.objects */ >>> >>> This is == OO_MASK right? Otherwise things will break when we change >>> OO_SHIFT. >>> >> >> Yes, I set it 65535 directly to distinguish it from OO_MASK >> meaning not value and point to page.objects since they are >> u16. Which meant that is the point where all limits start. >> So it we set OO_SHIFT to say 14 it will not be a problem >> but if we exceed 16 bits it will break SLUB. Am I right? >> (I become scratching the head :) > > If you set it > 16 then the size of the field in struct page is violated. > > So > > #define MAX_OBJ_PER_PAGE MIN(1 << bits_in(page.objects) - 1, OO_MASK) > > ? > >
Looks really good for me (if it worth anything). But Christoph doesn't OO_SHIT inspired by u16 too which means we could use MAX_OBJ_PER_PAGE in form you mentoined but maybe we should define
#define OO_SHIFT bits_in(page.objects) to point out why we use 16 not 14, not 18 or whatever? How do you think?
- Cyrill -
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