• Kirill A. Shutemov's avatar
    thp: reintroduce split_huge_page() · e9b61f19
    Kirill A. Shutemov authored
    This patch adds implementation of split_huge_page() for new
    refcountings.
    
    Unlike previous implementation, new split_huge_page() can fail if
    somebody holds GUP pin on the page.  It also means that pin on page
    would prevent it from bening split under you.  It makes situation in
    many places much cleaner.
    
    The basic scheme of split_huge_page():
    
      - Check that sum of mapcounts of all subpage is equal to page_count()
        plus one (caller pin). Foll off with -EBUSY. This way we can avoid
        useless PMD-splits.
    
      - Freeze the page counters by splitting all PMD and setup migration
        PTEs.
    
      - Re-check sum of mapcounts against page_count(). Page's counts are
        stable now. -EBUSY if page is pinned.
    
      - Split compound page.
    
      - Unfreeze the page by removing migration entries.
    Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Tested-by: default avatarSasha Levin <sasha.levin@oracle.com>
    Tested-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Acked-by: default avatarJerome Marchand <jmarchan@redhat.com>
    Cc: Vlastimil Babka <vbabka@suse.cz>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Dave Hansen <dave.hansen@intel.com>
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Cc: Steve Capper <steve.capper@linaro.org>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Michal Hocko <mhocko@suse.cz>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: David Rientjes <rientjes@google.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    e9b61f19
huge_mm.h 6.23 KB