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mm/sparse.c: add a static variable nr_present_sections 

Patch series "mm/sparse: Optimize memmap allocation during
sparse_init()", v6.

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.

This patch (of 5):

nr_present_sections is used to record how many memory sections are
marked as present during system boot up, and will be used in the later
patch.

Link: http://lkml.kernel.org/r/20180228032657.32385-2-bhe@redhat.com
Signed-off-by: Baoquan He <bhe@redhat.com>
Acked-by: Dave Hansen <dave.hansen@intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Pasha Tatashin <Pavel.Tatashin@microsoft.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Pankaj Gupta <pagupta@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Baoquan He 2018-08-17 15:48:38 -07:00 committed by Linus Torvalds
parent 7e010df53c
commit f2fc10e0b3
1 changed files with 7 additions and 0 deletions
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7
mm/sparse.c
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@ -200,6 +200,12 @@ static inline int next_present_section_nr(int section_nr)
(section_nr <= __highest_present_section_nr)); \
section_nr = next_present_section_nr(section_nr))
/*
* Record how many memory sections are marked as present
* during system bootup.
*/
static int __initdata nr_present_sections;
/* Record a memory area against a node. */
void __init memory_present(int nid, unsigned long start, unsigned long end)
{
@ -229,6 +235,7 @@ void __init memory_present(int nid, unsigned long start, unsigned long end)
ms->section_mem_map = sparse_encode_early_nid(nid) |
SECTION_IS_ONLINE;
section_mark_present(ms);
nr_present_sections++;
}
}
}