[Cc Dave who has added the lock into this path. Maybe he remembers why]
On Tue 27-11-18 10:36:30, Wei Yang wrote:
> pgdat_resize_lock is used to protect pgdat's memory region information
> like: node_start_pfn, node_present_pages, etc.
>
> In function sparse_add/remove_one_section(), those data is not touched.
> This means it is not necessary to acquire pgdat_resize_lock to protect
> this area.
>
> Since the information needed in sparse_add_one_section() is node id to
> allocate proper memory. This patch also changes the prototype of
> sparse_add_one_section() to pass node id directly. This is intended to
> reduce misleading that sparse_add_one_section() would touch pgdat.
>
> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
> ---
> include/linux/memory_hotplug.h | 2 +-
> mm/memory_hotplug.c | 2 +-
> mm/sparse.c | 17 +++++------------
> 3 files changed, 7 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 45a5affcab8a..3787d4e913e6 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -333,7 +333,7 @@ extern void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
> unsigned long nr_pages, struct vmem_altmap *altmap);
> extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
> extern bool is_memblock_offlined(struct memory_block *mem);
> -extern int sparse_add_one_section(struct pglist_data *pgdat,
> +extern int sparse_add_one_section(int nid,
> unsigned long start_pfn, struct vmem_altmap *altmap);
> extern void sparse_remove_one_section(struct zone *zone, struct mem_section *ms,
> unsigned long map_offset, struct vmem_altmap *altmap);
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index f626e7e5f57b..5b3a3d7b4466 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -253,7 +253,7 @@ static int __meminit __add_section(int nid, unsigned long phys_start_pfn,
> if (pfn_valid(phys_start_pfn))
> return -EEXIST;
>
> - ret = sparse_add_one_section(NODE_DATA(nid), phys_start_pfn, altmap);
> + ret = sparse_add_one_section(nid, phys_start_pfn, altmap);
> if (ret < 0)
> return ret;
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 33307fc05c4d..a4fdbcb21514 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -662,25 +662,24 @@ static void free_map_bootmem(struct page *memmap)
> * set. If this is <=0, then that means that the passed-in
> * map was not consumed and must be freed.
> */
> -int __meminit sparse_add_one_section(struct pglist_data *pgdat,
> - unsigned long start_pfn, struct vmem_altmap *altmap)
> +int __meminit sparse_add_one_section(int nid, unsigned long start_pfn,
> + struct vmem_altmap *altmap)
> {
> unsigned long section_nr = pfn_to_section_nr(start_pfn);
> struct mem_section *ms;
> struct page *memmap;
> unsigned long *usemap;
> - unsigned long flags;
> int ret;
>
> /*
> * no locking for this, because it does its own
> * plus, it does a kmalloc
> */
> - ret = sparse_index_init(section_nr, pgdat->node_id);
> + ret = sparse_index_init(section_nr, nid);
> if (ret < 0 && ret != -EEXIST)
> return ret;
> ret = 0;
> - memmap = kmalloc_section_memmap(section_nr, pgdat->node_id, altmap);
> + memmap = kmalloc_section_memmap(section_nr, nid, altmap);
> if (!memmap)
> return -ENOMEM;
> usemap = __kmalloc_section_usemap();
> @@ -689,8 +688,6 @@ int __meminit sparse_add_one_section(struct pglist_data *pgdat,
> return -ENOMEM;
> }
>
> - pgdat_resize_lock(pgdat, &flags);
> -
> ms = __pfn_to_section(start_pfn);
> if (ms->section_mem_map & SECTION_MARKED_PRESENT) {
> ret = -EEXIST;
> @@ -707,7 +704,6 @@ int __meminit sparse_add_one_section(struct pglist_data *pgdat,
> sparse_init_one_section(ms, section_nr, memmap, usemap);
>
> out:
> - pgdat_resize_unlock(pgdat, &flags);
> if (ret < 0) {
> kfree(usemap);
> __kfree_section_memmap(memmap, altmap);
> @@ -769,10 +765,8 @@ void sparse_remove_one_section(struct zone *zone, struct mem_section *ms,
> unsigned long map_offset, struct vmem_altmap *altmap)
> {
> struct page *memmap = NULL;
> - unsigned long *usemap = NULL, flags;
> - struct pglist_data *pgdat = zone->zone_pgdat;
> + unsigned long *usemap = NULL;
>
> - pgdat_resize_lock(pgdat, &flags);
> if (ms->section_mem_map) {
> usemap = ms->pageblock_flags;
> memmap = sparse_decode_mem_map(ms->section_mem_map,
> @@ -780,7 +774,6 @@ void sparse_remove_one_section(struct zone *zone, struct mem_section *ms,
> ms->section_mem_map = 0;
> ms->pageblock_flags = NULL;
> }
> - pgdat_resize_unlock(pgdat, &flags);
>
> clear_hwpoisoned_pages(memmap + map_offset,
> PAGES_PER_SECTION - map_offset);
> --
> 2.15.1
>
--
Michal Hocko
SUSE Labs
