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Subject[PATCH v3 0/4] mm/sparse: Optimize memmap allocation during sparse_init()
This is v3 post. V1 can be found here:

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

Change log:
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.

Split out the nr_present_sections adding as a single patch for easier

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
mm/sparse: Optimize memmap allocation during sparse_init()

mm/sparse-vmemmap.c | 6 +++---
mm/sparse.c | 62 ++++++++++++++++++++++++++++++++++++++---------------
2 files changed, 48 insertions(+), 20 deletions(-)


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