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

Baoquan He
2018-06-28T06:29:09Z

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@redhat.com
v4:
http://lkml.kernel.org/r/20180521101555.25610-1-bhe@redhat.com

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