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

--
Michal Hocko
SUSE Labs

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