linux-kernel - [PATCH v2 0/3] mm/sparse: Optimize memmap allocation during sparse

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Message-Id: <20180222091130.32165-1-bhe@redhat.com>
Date:   Thu, 22 Feb 2018 17:11:27 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org, dave.hansen@...el.com
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        kirill.shutemov@...ux.intel.com, mhocko@...e.com,
        tglx@...utronix.de, Baoquan He <bhe@...hat.com>
Subject: [PATCH v2 0/3] mm/sparse: Optimize memmap allocation during sparse_init()

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(-)

-- 
2.13.6