The patch titled
Subject: mm/sparse: remove index_init_lock
has been added to the -mm tree. Its filename is
mm-sparse-remove-index_init_lock.patch
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From: Gavin Shan <shangw@xxxxxxxxxxxxxxxxxx>
Subject: mm/sparse: remove index_init_lock
sparse_index_init() uses the index_init_lock spinlock to protect root
mem_section assignment. The lock is not necessary anymore because the
function is called only during 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 was 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 was 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.
[mhocko@xxxxxxx: changelog]
Signed-off-by: Gavin Shan <shangw@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/sparse.c | 14 +-------------
1 file changed, 1 insertion(+), 13 deletions(-)
diff -puN mm/sparse.c~mm-sparse-remove-index_init_lock mm/sparse.c
--- a/mm/sparse.c~mm-sparse-remove-index_init_lock
+++ a/mm/sparse.c
@@ -77,7 +77,6 @@ static struct mem_section noinline __ini
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(u
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 */
_
Subject: Subject: mm/sparse: remove index_init_lock
Patches currently in -mm which might be from shangw@xxxxxxxxxxxxxxxxxx are
linux-next.patch
mm-slab-remove-duplicate-check.patch
mm-buddy-cleanup-on-should_fail_alloc_page.patch
mm-compaction-cleanup-on-compaction_deferred.patch
memcg-add-mem_cgroup_from_css-helper.patch
memcg-add-mem_cgroup_from_css-helper-fix.patch
memcg-add-mem_cgroup_from_css-helper-fix-2.patch
mm-sparse-optimize-sparse_index_alloc.patch
mm-sparse-more-check-on-mem_section-number.patch
mm-sparse-remove-index_init_lock.patch
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