mm/thp: define HPAGE_PMD_* constants as BUILD_BUG() if !THP

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Currently, HPAGE_PMD_* constans rely on PMD_SHIFT regardless of
CONFIG_TRANSPARENT_HUGEPAGE.  PMD_SHIFT is not defined everywhere (e.g.
arm nommu case).

It means we can't use anything like this in generic code:

        if (PageTransHuge(page))
                zero_huge_user(page, 0, HPAGE_PMD_SIZE);
        else
                clear_highpage(page);

For !THP case, PageTransHuge() is 0 and compiler can eliminate
zero_huge_user() call.  But it still need to be valid C expression, means
HPAGE_PMD_SIZE has to expand to something compiler can understand.

Previously, HPAGE_PMD_* were defined to BUILD_BUG() for !THP. Let's come
back to it.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

...

This commit is contained in:

Kirill A. Shutemov 2013-06-25 14:15:36 -07:00 • committed by Benjamin Herrenschmidt

parent 5459ae1431

commit 3766a1abc5

1 changed files with 5 additions and 1 deletions

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include/linux/huge_mm.h

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