• Roman Pen's avatar
    mm/vmalloc: get rid of dirty bitmap inside vmap_block structure · 7d61bfe8
    Roman Pen authored
    In original implementation of vm_map_ram made by Nick Piggin there were
    two bitmaps: alloc_map and dirty_map.  None of them were used as supposed
    to be: finding a suitable free hole for next allocation in block.
    vm_map_ram allocates space sequentially in block and on free call marks
    pages as dirty, so freed space can't be reused anymore.
    Actually it would be very interesting to know the real meaning of those
    bitmaps, maybe implementation was incomplete, etc.
    But long time ago Zhang Yanfei removed alloc_map by these two commits:
      mm/vmalloc.c: remove dead code in vb_alloc
      mm/vmalloc.c: remove alloc_map from vmap_block
    In this patch I replaced dirty_map with two range variables: dirty min and
    max.  These variables store minimum and maximum position of dirty space in
    a block, since we need only to know the dirty range, not exact position of
    dirty pages.
    Why it was made?  Several reasons: at first glance it seems that
    vm_map_ram allocator concerns about fragmentation thus it uses bitmaps for
    finding free hole, but it is not true.  To avoid complexity seems it is
    better to use something simple, like min or max range values.  Secondly,
    code also becomes simpler, without iteration over bitmap, just comparing
    values in min and max macros.  Thirdly, bitmap occupies up to 1024 bits
    (4MB is a max size of a block).  Here I replaced the whole bitmap with two
    Finally vm_unmap_aliases should be slightly faster and the whole
    vmap_block structure occupies less memory.
    Signed-off-by: default avatarRoman Pen <r.peniaev@gmail.com>
    Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
    Cc: Eric Dumazet <edumazet@google.com>
    Acked-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: WANG Chao <chaowang@redhat.com>
    Cc: Fabian Frederick <fabf@skynet.be>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Gioh Kim <gioh.kim@lge.com>
    Cc: Rob Jones <rob.jones@codethink.co.uk>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
vmalloc.c 69 KB