From: Baoquan He <bhe@xxxxxxxxxx> Subject: 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@xxxxxxxxxx Signed-off-by: Baoquan He <bhe@xxxxxxxxxx> Acked-by: Dave Hansen <dave.hansen@xxxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Reviewed-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx> Cc: Pasha Tatashin <Pavel.Tatashin@xxxxxxxxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Pankaj Gupta <pagupta@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/sparse.c | 7 +++++++ 1 file changed, 7 insertions(+) --- a/mm/sparse.c~mm-sparse-add-a-static-variable-nr_present_sections +++ a/mm/sparse.c @@ -200,6 +200,12 @@ static inline int next_present_section_n (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, unsi ms->section_mem_map = sparse_encode_early_nid(nid) | SECTION_IS_ONLINE; section_mark_present(ms); + nr_present_sections++; } } } _
