diff mbox series

[2/3] mm: sparse: pass section_nr to find_memory_block

Message ID 20210702094132.6276-3-ohoono.kwon@samsung.com (mailing list archive)
State New
Headers show
Series mm: sparse: remove __section_nr() function | expand

Commit Message

권오훈 July 2, 2021, 9:41 a.m. UTC
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>
---
 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(-)

Comments

Michal Hocko July 2, 2021, 12:17 p.m. UTC | #1
On Fri 02-07-21 18:41:31, Ohhoon Kwon wrote:
> 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.

Yeah, it seems like the only existing user (maybe there used to be more
in the past - haven't checked) is just doing pointless translation to
comply with the API that doesn't fit it. Just to undo all that work
in find_memory_block 

Nice cleanup and potentially even a performance improvement!
 
> Signed-off-by: Ohhoon Kwon <ohoono.kwon@samsung.com>

Acked-by: Michal Hocko <mhocko@suse.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 8377f1f7c78e..905790092e0e 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
David Hildenbrand July 2, 2021, 5:55 p.m. UTC | #2
On 02.07.21 11:41, Ohhoon Kwon wrote:
> 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>


Reviewed-by: David Hildenbrand <david@redhat.com>
diff mbox series

Patch

diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index 8377f1f7c78e..905790092e0e 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);