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    Subject[PATCH v5 0/4] mm/sparse: Optimize memmap allocation during sparse_init()
    Date
    This is v4 post. V3 can be found here:
    https://lkml.org/lkml/2018/2/27/928

    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
    CONFIG_X86_5LEVEL=y.

    Change log:
    v4->v5:
    Improve patch 3/4 log according to Dave's suggestion.

    Correct the wrong copy&paste of making 'nr_consumed_maps' to
    'alloc_usemap_and_memmap' mistakenly which is pointed out by
    Dave in patch 4/4 code comment.

    Otherwise, no code change in this version.
    v3->v4:
    Improve according to Dave's three concerns which are in patch 0004:

    Rename variable 'idx_present' to 'nr_consumed_maps' which used to
    index the memmap and usemap of present sections.

    Add a check if 'nr_consumed_maps' goes beyond nr_present_sections.

    Add code comment above the final for_each_present_section_nr() to
    tell why 'nr_consumed_maps' need be increased in each iteration
    whether the 'ms->section_mem_map' need cleared or out.

    v2->v3:
    Change nr_present_sections as __initdata and add code comment
    according to Andrew's suggestion.

    Change the local variable 'i' as idx_present which loops over the
    present sections, and improve the code. These are suggested by
    Dave and Pankaj.

    Add a new patch 0003 which adds a new parameter 'data_unit_size'
    to function alloc_usemap_and_memmap() in which we will update 'data'
    to make it point at new position. However its type 'void *' can't give
    us needed info to do that. Need pass the unit size in. So change code
    in patch 0004 accordingly. This is a code bug fix found when tested
    the memory deployed on multiple nodes.

    v1-v2:
    Split out the nr_present_sections adding as a single patch for easier
    reviewing.

    Rewrite patch log according to Dave's suggestion.

    Fix code bug in patch 0002 reported by test robot.

    Baoquan He (4):
    mm/sparse: Add a static variable nr_present_sections
    mm/sparsemem: Defer the ms->section_mem_map clearing
    mm/sparse: Add a new parameter 'data_unit_size' for
    alloc_usemap_and_memmap
    mm/sparse: Optimize memmap allocation during sparse_init()

    mm/sparse-vmemmap.c | 6 ++---
    mm/sparse.c | 72 +++++++++++++++++++++++++++++++++++++++++------------
    2 files changed, 59 insertions(+), 19 deletions(-)

    --
    2.13.6

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