On 02/22/18 at 05:11pm, Baoquan He wrote:
> This is v2 post. V1 can be found here:
> https://www.spinics.net/lists/linux-mm/msg144486.html
> In sparse_init(), two temporary pointer arrays, usemap_map and map_map
> are allocated with the size of NR_MEM_SECTIONS. They are used to store
> each memory section's usemap and mem map if marked as present. In
> 5-level paging mode, this will cost 512M memory though they will be
> released at the end of sparse_init(). System with few memory, like
> kdump kernel which usually only has about 256M, will fail to boot
> because of allocation failure if CONFIG_X86_5LEVEL=y.
> In this patchset, optimize the memmap allocation code to only use
> usemap_map and map_map with the size of nr_present_sections. This
> makes kdump kernel boot up with normal crashkernel='' setting when

Sorry, forgot adding the change log.

  Split out the nr_present_sections adding as a single patch for easier

  Rewrite patch log according to Dave's suggestion.

  Fix code bug in patch 0002 reported by test robot.

> Baoquan He (3):
>   mm/sparse: Add a static variable nr_present_sections
>   mm/sparsemem: Defer the ms->section_mem_map clearing
>   mm/sparse: Optimize memmap allocation during sparse_init()
>  mm/sparse-vmemmap.c |  9 +++++----
>  mm/sparse.c         | 54 
> +++++++++++++++++++++++++++++++++++------------------
>  2 files changed, 41 insertions(+), 22 deletions(-)
> -- 
> 2.13.6

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