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    nommu: clamp zone_batchsize() to 0 under NOMMU conditions · 3a6be87f
    David Howells 提交于
    Clamp zone_batchsize() to 0 under NOMMU conditions to stop
    free_hot_cold_page() from queueing and batching frees.
    
    The problem is that under NOMMU conditions it is really important to be
    able to allocate large contiguous chunks of memory, but when munmap() or
    exit_mmap() releases big stretches of memory, return of these to the buddy
    allocator can be deferred, and when it does finally happen, it can be in
    small chunks.
    
    Whilst the fragmentation this incurs isn't so much of a problem under MMU
    conditions as userspace VM is glued together from individual pages with
    the aid of the MMU, it is a real problem if there isn't an MMU.
    
    By clamping the page freeing queue size to 0, pages are returned to the
    allocator immediately, and the buddy detector is more likely to be able to
    glue them together into large chunks immediately, and fragmentation is
    less likely to occur.
    
    By disabling batching of frees, and by turning off the trimming of excess
    space during boot, Coldfire can manage to boot.
    Reported-by: NLanttor Guo <lanttor.guo@freescale.com>
    Signed-off-by: NDavid Howells <dhowells@redhat.com>
    Tested-by: NLanttor Guo <lanttor.guo@freescale.com>
    Cc: Greg Ungerer <gerg@snapgear.com>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    3a6be87f
page_alloc.c 131.2 KB