[132/212] mm: sparse: pass section_nr to find_memory_block

Commit Message

Andrew Morton Sept. 2, 2021, 9:57 p.m. UTC

From: Ohhoon Kwon <[e-mail]>
Subject: mm: sparse: pass section_nr to find_memory_block

With CONFIG_SPARSEMEM_EXTREME enabled, __section_nr() which converts
mem_section to section_nr could be costly since it iterates all section
roots to check if the given mem_section is in its range.

On the other hand, __nr_to_section() which converts section_nr to
mem_section can be done in O(1).

Let's pass section_nr instead of mem_section ptr to find_memory_block() in
order to reduce needless iterations.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ohhoon Kwon <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Acked-by: Mike Rapoport <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Cc: Baoquan He <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 arch/powerpc/platforms/pseries/hotplug-memory.c |    4 +---
 drivers/base/memory.c                           |    4 ++--
 include/linux/memory.h                          |    2 +-
 3 files changed, 4 insertions(+), 6 deletions(-)

Patch

--- a/arch/powerpc/platforms/pseries/hotplug-memory.c~mm-sparse-pass-section_nr-to-find_memory_block
+++ a/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -211,13 +211,11 @@  static int update_lmb_associativity_inde
 static struct memory_block *lmb_to_memblock(struct drmem_lmb *lmb)
 {
 	unsigned long section_nr;
-	struct mem_section *mem_sect;
 	struct memory_block *mem_block;
 
 	section_nr = pfn_to_section_nr(PFN_DOWN(lmb->base_addr));
-	mem_sect = __nr_to_section(section_nr);
 
-	mem_block = find_memory_block(mem_sect);
+	mem_block = find_memory_block(section_nr);
 	return mem_block;
 }
 
--- a/drivers/base/memory.c~mm-sparse-pass-section_nr-to-find_memory_block
+++ a/drivers/base/memory.c
@@ -578,9 +578,9 @@  static struct memory_block *find_memory_
 /*
  * Called under device_hotplug_lock.
  */
-struct memory_block *find_memory_block(struct mem_section *section)
+struct memory_block *find_memory_block(unsigned long section_nr)
 {
-	unsigned long block_id = memory_block_id(__section_nr(section));
+	unsigned long block_id = memory_block_id(section_nr);
 
 	return find_memory_block_by_id(block_id);
 }
--- a/include/linux/memory.h~mm-sparse-pass-section_nr-to-find_memory_block
+++ a/include/linux/memory.h
@@ -90,7 +90,7 @@  int create_memory_block_devices(unsigned
 void remove_memory_block_devices(unsigned long start, unsigned long size);
 extern void memory_dev_init(void);
 extern int memory_notify(unsigned long val, void *v);
-extern struct memory_block *find_memory_block(struct mem_section *);
+extern struct memory_block *find_memory_block(unsigned long section_nr);
 typedef int (*walk_memory_blocks_func_t)(struct memory_block *, void *);
 extern int walk_memory_blocks(unsigned long start, unsigned long size,
 			      void *arg, walk_memory_blocks_func_t func);