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/[email protected]
Signed-off-by: Baoquan He <[email protected]>
Acked-by: Dave Hansen <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Reviewed-by: Pavel Tatashin <[email protected]>
Reviewed-by: Oscar Salvador <[email protected]>
Cc: Pasha Tatashin <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Pankaj Gupta <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/sparse.c b/mm/sparse.c
index b1b14a9c4041ec05810c9341f23ff5f0c3f00343..99a6383e98bc73ecd345263308b7e25eb9849a2e 100644 (file)
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -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++;
                }
        }
 }