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Subject[PATCH v4 2/3] mm: sparse: pass section_nr to find_memory_block
Date
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.

Signed-off-by: Ohhoon Kwon <ohoono.kwon@samsung.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
---
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(-)

diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index 377d852f5a9a..d4f28ee4d5dc 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -211,13 +211,11 @@ static int update_lmb_associativity_index(struct drmem_lmb *lmb)
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;
}

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index d5ffaab3cb61..e31598955cc4 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -578,9 +578,9 @@ static struct memory_block *find_memory_block_by_id(unsigned long block_id)
/*
* 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);
}
diff --git a/include/linux/memory.h b/include/linux/memory.h
index 97e92e8b556a..d9a0b61cd432 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -90,7 +90,7 @@ int create_memory_block_devices(unsigned long start, unsigned long size,
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);
--
2.17.1
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