• Mel Gorman's avatar
    Create the ZONE_MOVABLE zone · 2a1e274a
    Mel Gorman authored
    The following 8 patches against 2.6.20-mm2 create a zone called ZONE_MOVABLE
    that is only usable by allocations that specify both __GFP_HIGHMEM and
    __GFP_MOVABLE.  This has the effect of keeping all non-movable pages within a
    single memory partition while allowing movable allocations to be satisfied
    from either partition.  The patches may be applied with the list-based
    anti-fragmentation patches that groups pages together based on mobility.
    
    The size of the zone is determined by a kernelcore= parameter specified at
    boot-time.  This specifies how much memory is usable by non-movable
    allocations and the remainder is used for ZONE_MOVABLE.  Any range of pages
    within ZONE_MOVABLE can be released by migrating the pages or by reclaiming.
    
    When selecting a zone to take pages from for ZONE_MOVABLE, there are two
    things to consider.  First, only memory from the highest populated zone is
    used for ZONE_MOVABLE.  On the x86, this is probably going to be ZONE_HIGHMEM
    but it would be ZONE_DMA on ppc64 or possibly ZONE_DMA32 on x86_64.  Second,
    the amount of memory usable by the kernel will be spread evenly throughout
    NUMA nodes where possible.  If the nodes are not of equal size, the amount of
    memory usable by the kernel on some nodes may be greater than others.
    
    By default, the zone is not as useful for hugetlb allocations because they are
    pinned and non-migratable (currently at least).  A sysctl is provided that
    allows huge pages to be allocated from that zone.  This means that the huge
    page pool can be resized to the size of ZONE_MOVABLE during the lifetime of
    the system assuming that pages are not mlocked.  Despite huge pages being
    non-movable, we do not introduce additional external fragmentation of note as
    huge pages are always the largest contiguous block we care about.
    
    Credit goes to Andy Whitcroft for catching a large variety of problems during
    review of the patches.
    
    This patch creates an additional zone, ZONE_MOVABLE.  This zone is only usable
    by allocations which specify both __GFP_HIGHMEM and __GFP_MOVABLE.  Hot-added
    memory continues to be placed in their existing destination as there is no
    mechanism to redirect them to a specific zone.
    
    [y-goto@jp.fujitsu.com: Fix section mismatch of memory hotplug related code]
    [akpm@linux-foundation.org: various fixes]
    Signed-off-by: default avatarMel Gorman <mel@csn.ul.ie>
    Cc: Andy Whitcroft <apw@shadowen.org>
    Signed-off-by: default avatarYasunori Goto <y-goto@jp.fujitsu.com>
    Cc: William Lee Irwin III <wli@holomorphy.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    2a1e274a
vmstat.c 16.9 KB