On Fri 13-07-12 10:01:22, Gavin Shan wrote:
> sparse_index_init uses index_init_lock spinlock to protect root
> mem_section assignment. The lock is not necessary anymore because the
> function is called only during the boot (during paging init which
> is executed only from a single CPU) and from the hotplug code (by
> add_memory via arch_add_memory) which uses mem_hotplug_mutex.
>
> The lock has been introduced by 28ae55c9 (sparsemem extreme: hotplug
> preparation) and sparse_index_init was used only during boot at that
> time.
>
> Later when the hotplug code (and add_memory) was introduced there was
> no synchronization so it was possible to online more sections from
> the same root probably (though I am not 100% sure about that).
> The first synchronization has been added by 6ad696d2 (mm: allow memory
> hotplug and hibernation in the same kernel) which has been later
> replaced by the mem_hotplug_mutex - 20d6c96b (mem-hotplug: introduce
> {un}lock_memory_hotplug()).
>
> Let's remove the lock as it is not needed and it makes the code more
> confusing.
>
> Signed-off-by: Gavin Shan <shangw@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> mm/sparse.c | 14 +-------------
> 1 files changed, 1 insertions(+), 13 deletions(-)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 51950de..40b1100 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -77,7 +77,6 @@ static struct mem_section noinline __init_refok *sparse_index_alloc(int nid)
>
> static int __meminit sparse_index_init(unsigned long section_nr, int nid)
> {
> - static DEFINE_SPINLOCK(index_init_lock);
> unsigned long root = SECTION_NR_TO_ROOT(section_nr);
> struct mem_section *section;
> int ret = 0;
> @@ -88,20 +87,9 @@ static int __meminit sparse_index_init(unsigned long section_nr, int nid)
> section = sparse_index_alloc(nid);
> if (!section)
> return -ENOMEM;
> - /*
> - * This lock keeps two different sections from
> - * reallocating for the same index
> - */
> - spin_lock(&index_init_lock);
> -
> - if (mem_section[root]) {
> - ret = -EEXIST;
> - goto out;
> - }
>
> mem_section[root] = section;
> -out:
> - spin_unlock(&index_init_lock);
> +
> return ret;
> }
> #else /* !SPARSEMEM_EXTREME */
> --
> 1.7.5.4
>
> --
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--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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