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Subject[PATCH 4.14 023/159] mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

commit 83e3c48729d9ebb7af5a31a504f3fd6aff0348c4 upstream.

Size of the mem_section[] array depends on the size of the physical address space.

In preparation for boot-time switching between paging modes on x86-64
we need to make the allocation of mem_section[] dynamic, because otherwise
we waste a lot of RAM: with CONFIG_NODE_SHIFT=10, mem_section[] size is 32kB
for 4-level paging and 2MB for 5-level paging mode.

The patch allocates the array on the first call to sparse_memory_present_with_active_regions().

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@suse.de>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20170929140821.37654-2-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/mmzone.h | 6 +++++-
mm/page_alloc.c | 10 ++++++++++
mm/sparse.c | 17 +++++++++++------
3 files changed, 26 insertions(+), 7 deletions(-)

--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1152,13 +1152,17 @@ struct mem_section {
#define SECTION_ROOT_MASK (SECTIONS_PER_ROOT - 1)

#ifdef CONFIG_SPARSEMEM_EXTREME
-extern struct mem_section *mem_section[NR_SECTION_ROOTS];
+extern struct mem_section **mem_section;
#else
extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
#endif

static inline struct mem_section *__nr_to_section(unsigned long nr)
{
+#ifdef CONFIG_SPARSEMEM_EXTREME
+ if (!mem_section)
+ return NULL;
+#endif
if (!mem_section[SECTION_NR_TO_ROOT(nr)])
return NULL;
return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5651,6 +5651,16 @@ void __init sparse_memory_present_with_a
unsigned long start_pfn, end_pfn;
int i, this_nid;

+#ifdef CONFIG_SPARSEMEM_EXTREME
+ if (!mem_section) {
+ unsigned long size, align;
+
+ size = sizeof(struct mem_section) * NR_SECTION_ROOTS;
+ align = 1 << (INTERNODE_CACHE_SHIFT);
+ mem_section = memblock_virt_alloc(size, align);
+ }
+#endif
+
for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, &this_nid)
memory_present(this_nid, start_pfn, end_pfn);
}
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -23,8 +23,7 @@
* 1) mem_section - memory sections, mem_map's for valid memory
*/
#ifdef CONFIG_SPARSEMEM_EXTREME
-struct mem_section *mem_section[NR_SECTION_ROOTS]
- ____cacheline_internodealigned_in_smp;
+struct mem_section **mem_section;
#else
struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT]
____cacheline_internodealigned_in_smp;
@@ -101,7 +100,7 @@ static inline int sparse_index_init(unsi
int __section_nr(struct mem_section* ms)
{
unsigned long root_nr;
- struct mem_section* root;
+ struct mem_section *root = NULL;

for (root_nr = 0; root_nr < NR_SECTION_ROOTS; root_nr++) {
root = __nr_to_section(root_nr * SECTIONS_PER_ROOT);
@@ -112,7 +111,7 @@ int __section_nr(struct mem_section* ms)
break;
}

- VM_BUG_ON(root_nr == NR_SECTION_ROOTS);
+ VM_BUG_ON(!root);

return (root_nr * SECTIONS_PER_ROOT) + (ms - root);
}
@@ -330,11 +329,17 @@ again:
static void __init check_usemap_section_nr(int nid, unsigned long *usemap)
{
unsigned long usemap_snr, pgdat_snr;
- static unsigned long old_usemap_snr = NR_MEM_SECTIONS;
- static unsigned long old_pgdat_snr = NR_MEM_SECTIONS;
+ static unsigned long old_usemap_snr;
+ static unsigned long old_pgdat_snr;
struct pglist_data *pgdat = NODE_DATA(nid);
int usemap_nid;

+ /* First call */
+ if (!old_usemap_snr) {
+ old_usemap_snr = NR_MEM_SECTIONS;
+ old_pgdat_snr = NR_MEM_SECTIONS;
+ }
+
usemap_snr = pfn_to_section_nr(__pa(usemap) >> PAGE_SHIFT);
pgdat_snr = pfn_to_section_nr(__pa(pgdat) >> PAGE_SHIFT);
if (usemap_snr == pgdat_snr)

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