• Christoph Lameter's avatar
    [PATCH] reduce MAX_NR_ZONES: remove two strange uses of MAX_NR_ZONES · 776ed98b
    Christoph Lameter authored
    I keep seeing zones on various platforms that are never used and wonder why we
    compile support for them into the kernel.  Counters show up for HIGHMEM and
    DMA32 that are alway zero.
    
    This patch allows the removal of ZONE_DMA32 for non x86_64 architectures and
    it will get rid of ZONE_HIGHMEM for arches not using highmem (like 64 bit
    architectures).  If an arch does not define CONFIG_HIGHMEM then ZONE_HIGHMEM
    will not be defined.  Similarly if an arch does not define CONFIG_ZONE_DMA32
    then ZONE_DMA32 will not be defined.
    
    No current architecture uses all the 4 zones (DMA,DMA32,NORMAL,HIGH) that we
    have now.  The patchset will reduce the number of zones for all platforms.
    
    On many platforms that do not have DMA32 or HIGHMEM this will reduce the
    number of zones by 50%.  F.e.  ia64 only uses DMA and NORMAL.
    
    Large amounts of memory can be saved for larger systemss that may have a few
    hundred NUMA nodes.
    
    With ZONE_DMA32 and ZONE_HIGHMEM support optional MAX_NR_ZONES will be 2 for
    many non i386 platforms and even for i386 without CONFIG_HIGHMEM set.
    
    Tested on ia64, x86_64 and on i386 with and without highmem.
    
    The patchset consists of 11 patches that are following this message.
    
    One could go even further than this patchset and also make ZONE_DMA optional
    because some platforms do not need a separate DMA zone and can do DMA to all
    of memory.  This could reduce MAX_NR_ZONES to 1.  Such a patchset will
    hopefully follow soon.
    
    This patch:
    
    Fix strange uses of MAX_NR_ZONES
    
    Sometimes we use MAX_NR_ZONES - x to refer to a zone.  Make that explicit.
    Signed-off-by: default avatarChristoph Lameter <clameter@sgi.com>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    776ed98b
init.c 20.2 KB