Messages in this thread | | | Date | Thu, 17 Nov 2011 09:21:14 -0800 | From | David Daney <> | Subject | Re: [PATCH] hugetlb: Provide a default HPAGE_SHIFT if !CONFIG_HUGETLB_PAGE |
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On 11/16/2011 08:56 PM, David Rientjes wrote: > On Wed, 16 Nov 2011, David Daney wrote: > >>>> It is a well established kernel idiom to supply dummy values for symbols >>>> that >>>> are required to be defined in order to form a syntactically correct C >>>> program, >>>> but that are known by the programmer to be used only on dead code paths. >>>> >>>> This is exactly what we are doing here. >>>> >>>> To do otherwise requires that code be cluttered with #ifdefery. >>>> >>> >>> You're wrong, >> >> Ok, then please tell me why: >> >> 1) the dummy version of is_vm_hugetlb_page() exists in hugetlb_inline.h? >> 2) the dummy version of PageHuge() exists in hugetlb.h [...] > > To avoid the #ifdef's,
Good, now we are on the same page.
The answer is not, as first suggested, to sprinkle #ifdefs all over the place, but ...
> but you'll notice that they return either NULL, 0, > or are a no-op. We don't substitute real values in dummy functions where > they could be used in generic code as though they were valid. That's the > problem with defining HPAGE_SHIFT to be PAGE_SHIFT and, yes, defining > HPAGE_MASK and HPAGE_SIZE as well shouldn't be done and should be removed. > > We expect HPAGE_* to represent hugepages, not the native page size of the > bare metal. This is why we do things like > > #define HPAGE_PMD_SHIFT ({ BUG(); 0; }) > #define HPAGE_PMD_MASK ({ BUG(); 0; }) > #define HPAGE_PMD_SIZE ({ BUG(); 0; })
... rather to fix HPAGE_SHIFT, HPAGE_MASK, and HPAGE_SIZE to be more like these.
I will generate a version of the patch that does this, noting that it the addition of a dummy definition of HPAGE_SHIFT is added to facilitate cleaner architecture specific code for MIPS patches in linux-next.
Thanks, David Daney
> > for CONFIG_TRANSPARENT_HUGEPAGE=n. We don't want to pretend that they're > valid outside the context of hugepages. > > We also never use HPAGE_SHIFT, HPAGE_MASK, or HPAGE_SIZE in generic code > that isn't dependent on CONFIG_HUGETLB_PAGE. If you'd like to submit a > patch to fix this in the mips tree, then that would be good, and if you'd > like to submit a patch to remove these dummy definitions all together by > auditing other arch code, then that would be great. >
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