[PATCH v4 0/4] mm/sparse: Optimize memmap allocation during sparse_init()

[Baoquan He <bhe@redhat.com>]

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:
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