• Naoya Horiguchi's avatar
    mm/hugetlb: reduce arch dependent code around follow_huge_* · 61f77eda
    Naoya Horiguchi authored
    Currently we have many duplicates in definitions around
    follow_huge_addr(), follow_huge_pmd(), and follow_huge_pud(), so this
    patch tries to remove the m.  The basic idea is to put the default
    implementation for these functions in mm/hugetlb.c as weak symbols
    (regardless of CONFIG_ARCH_WANT_GENERAL_HUGETL B), and to implement
    arch-specific code only when the arch needs it.
    
    For follow_huge_addr(), only powerpc and ia64 have their own
    implementation, and in all other architectures this function just returns
    ERR_PTR(-EINVAL).  So this patch sets returning ERR_PTR(-EINVAL) as
    default.
    
    As for follow_huge_(pmd|pud)(), if (pmd|pud)_huge() is implemented to
    always return 0 in your architecture (like in ia64 or sparc,) it's never
    called (the callsite is optimized away) no matter how implemented it is.
    So in such architectures, we don't need arch-specific implementation.
    
    In some architecture (like mips, s390 and tile,) their current
    arch-specific follow_huge_(pmd|pud)() are effectively identical with the
    common code, so this patch lets these architecture use the common code.
    
    One exception is metag, where pmd_huge() could return non-zero but it
    expects follow_huge_pmd() to always return NULL.  This means that we need
    arch-specific implementation which returns NULL.  This behavior looks
    strange to me (because non-zero pmd_huge() implies that the architecture
    supports PMD-based hugepage, so follow_huge_pmd() can/should return some
    relevant value,) but that's beyond this cleanup patch, so let's keep it.
    
    Justification of non-trivial changes:
    - in s390, follow_huge_pmd() checks !MACHINE_HAS_HPAGE at first, and this
      patch removes the check. This is OK because we can assume MACHINE_HAS_HPAGE
      is true when follow_huge_pmd() can be called (note that pmd_huge() has
      the same check and always returns 0 for !MACHINE_HAS_HPAGE.)
    - in s390 and mips, we use HPAGE_MASK instead of PMD_MASK as done in common
      code. This patch forces these archs use PMD_MASK, but it's OK because
      they are identical in both archs.
      In s390, both of HPAGE_SHIFT and PMD_SHIFT are 20.
      In mips, HPAGE_SHIFT is defined as (PAGE_SHIFT + PAGE_SHIFT - 3) and
      PMD_SHIFT is define as (PAGE_SHIFT + PAGE_SHIFT + PTE_ORDER - 3), but
      PTE_ORDER is always 0, so these are identical.
    Signed-off-by: default avatarNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Acked-by: default avatarHugh Dickins <hughd@google.com>
    Cc: James Hogan <james.hogan@imgtec.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Mel Gorman <mel@csn.ul.ie>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Michal Hocko <mhocko@suse.cz>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Luiz Capitulino <lcapitulino@redhat.com>
    Cc: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
    Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
    Cc: Steve Capper <steve.capper@linaro.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    61f77eda
hugetlbpage.c 4.94 KB