• Kirill A. Shutemov's avatar
    mm: drop tail page refcounting · ddc58f27
    Kirill A. Shutemov authored
    Tail page refcounting is utterly complicated and painful to support.
    It uses ->_mapcount on tail pages to store how many times this page is
    pinned.  get_page() bumps ->_mapcount on tail page in addition to
    ->_count on head.  This information is required by split_huge_page() to
    be able to distribute pins from head of compound page to tails during
    the split.
    We will need ->_mapcount to account PTE mappings of subpages of the
    compound page.  We eliminate need in current meaning of ->_mapcount in
    tail pages by forbidding split entirely if the page is pinned.
    The only user of tail page refcounting is THP which is marked BROKEN for
    Let's drop all this mess.  It makes get_page() and put_page() much
    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 avatarVlastimil Babka <vbabka@suse.cz>
    Acked-by: default avatarJerome Marchand <jmarchan@redhat.com>
    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>
gup.c 40.3 KB