[PATCH v6 0/5] mm/sparse: Optimize memmap allocation during sparse_init()

[Baoquan He]

This is v6 post.

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.

The old version can be found below:

v5:
http://lkml.kernel.org/r/20180627013116.12411-1-bhe@xxxxxxxxxx
v4:
http://lkml.kernel.org/r/20180521101555.25610-1-bhe@xxxxxxxxxx

v3:
https://lkml.org/lkml/2018/2/27/928

V1 can be found here:
https://www.spinics.net/lists/linux-mm/msg144486.html

Change log:
v5->v6:
  Oscar found the redundant "struct mem_section *ms" definition and
  in the old patch 2/4, after deferring the clearing of section_mem_map.
  Clean them up in this version.

  Pavel pointed out that allocating memmap together for one node at
  one time should be a default behaviour for all ARCH-es. And if failed
  on large memory, it will drop to the fallback to allocate memmap
  for one section at one time, it shoult not break anything. Add
  patch 5/5 to remove CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER and clean
  up the related codes.
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 (5):
  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: Remove CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER

 mm/Kconfig          |   4 --
 mm/sparse-vmemmap.c |   9 ++---
 mm/sparse.c         | 109 ++++++++++++++++++++++++++++------------------------
 3 files changed, 62 insertions(+), 60 deletions(-)

-- 
2.13.6