• Andrea Arcangeli's avatar
    mremap: avoid sending one IPI per page · 7b6efc2b
    Andrea Arcangeli authored
    This replaces ptep_clear_flush() with ptep_get_and_clear() and a single
    flush_tlb_range() at the end of the loop, to avoid sending one IPI for
    each page.
    
    The mmu_notifier_invalidate_range_start/end section is enlarged
    accordingly but this is not going to fundamentally change things.  It was
    more by accident that the region under mremap was for the most part still
    available for secondary MMUs: the primary MMU was never allowed to
    reliably access that region for the duration of the mremap (modulo
    trapping SIGSEGV on the old address range which sounds unpractical and
    flakey).  If users wants secondary MMUs not to lose access to a large
    region under mremap they should reduce the mremap size accordingly in
    userland and run multiple calls.  Overall this will run faster so it's
    actually going to reduce the time the region is under mremap for the
    primary MMU which should provide a net benefit to apps.
    
    For KVM this is a noop because the guest physical memory is never
    mremapped, there's just no point it ever moving it while guest runs.  One
    target of this optimization is JVM GC (so unrelated to the mmu notifier
    logic).
    Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
    Acked-by: default avatarJohannes Weiner <jweiner@redhat.com>
    Acked-by: default avatarMel Gorman <mgorman@suse.de>
    Acked-by: default avatarRik van Riel <riel@redhat.com>
    Cc: Hugh Dickins <hughd@google.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    7b6efc2b
mremap.c 13.3 KB