[PATCH v2 0/3] mm/sparse: Optimize memmap allocation during sparse_init()

From: Baoquan He
Date: Thu Feb 22 2018 - 04:12:49 EST


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
CONFIG_X86_5LEVEL=y.

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(-)

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2.13.6