Messages in this thread Patch in this message | | | Date | Wed, 17 Nov 2004 14:13:10 +1100 | From | Nick Piggin <> | Subject | Re: [RFC] Making compound pages mandatory |
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Andrew Morton wrote: > Linus Torvalds <torvalds@osdl.org> wrote: > >> >> >>On Tue, 16 Nov 2004, David Howells wrote: >> >>>Do you have any objection to compound pages being made mandatory, even without >>>HUGETLB support? >> >>I haven't really looked into it, so I cannot make an informed decision. >>How big is the overhead? And what's the _point_, since we don't seem to >>need them normally, but the code is there for people who _do_ need them? > > > Yes, it's just the single pointer chase. Probably that's the common case > now, because everyone will be enabling hugepages on lots of architectures. > > But still, the non-compound code is well tested too, and leaving it in > place does make a little microoptimisation available to those who want it, > so I don't see a reason yet to make compound pages compulsory. > > So I'd suggest that we make compound pages conditional on a new > CONFIG_COMPOUND_PAGE and make that equal to HUGETLB_PAGE || !MMU.
Good idea. BTW, any reason why the following (very)micro optimisation shouldn't go in?
It currently only picks up a couple of things under fs/, but might help reduce other ifdefery around the place. For example mm.h: page_count and get_page.
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linux-2.6-npiggin/include/linux/page-flags.h | 4 ++++ 1 files changed, 4 insertions(+)
diff -puN include/linux/page-flags.h~mm-page_compound-microopt include/linux/page-flags.h --- linux-2.6/include/linux/page-flags.h~mm-page_compound-microopt 2004-11-17 14:02:44.000000000 +1100 +++ linux-2.6-npiggin/include/linux/page-flags.h 2004-11-17 14:09:07.000000000 +1100 @@ -286,7 +286,11 @@ extern unsigned long __read_page_state(u #define ClearPageReclaim(page) clear_bit(PG_reclaim, &(page)->flags) #define TestClearPageReclaim(page) test_and_clear_bit(PG_reclaim, &(page)->flags) +#ifdef CONFIG_HUGETLB_PAGE #define PageCompound(page) test_bit(PG_compound, &(page)->flags) +#else +#define PageCompound(page) 0 +#endif #define SetPageCompound(page) set_bit(PG_compound, &(page)->flags) #define ClearPageCompound(page) clear_bit(PG_compound, &(page)->flags) _
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