[PATCH RESEND v4 1/3] mm/sparse: optimize sparse_index_alloc

[PATCH RESEND v4 1/3] mm/sparse: optimize sparse_index_alloc

[Gavin Shan]

With CONFIG_SPARSEMEM_EXTREME, the two level of memory section
descriptors are allocated from slab or bootmem. When allocating
from slab, let slab/bootmem allocator to clear the memory chunk.
We needn't clear that explicitly.

Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Acked-by: David Rientjes <rientjes@google.com>
---
 mm/sparse.c |   10 ++++------
 1 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index c7bb952..d882e88 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -65,14 +65,12 @@ static struct mem_section noinline __init_refok *sparse_index_alloc(int nid)
 
 	if (slab_is_available()) {
 		if (node_state(nid, N_HIGH_MEMORY))
-			section = kmalloc_node(array_size, GFP_KERNEL, nid);
+			section = kzalloc_node(array_size, GFP_KERNEL, nid);
 		else
-			section = kmalloc(array_size, GFP_KERNEL);
-	} else
+			section = kzalloc(array_size, GFP_KERNEL);
+	} else {
 		section = alloc_bootmem_node(NODE_DATA(nid), array_size);
-
-	if (section)
-		memset(section, 0, array_size);
+	}
 
 	return section;
 }
-- 
1.7.5.4

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[PATCH RESEND v4 2/3] mm/sparse: more check on mem_section number

[Gavin Shan]

Function __section_nr() was implemented to retrieve the corresponding
memory section number according to its descriptor. It's possible that
the specified memory section descriptor isn't existing in the global
array. So here to add more check on that and report error for wrong
case.

Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
Acked-by: David Rientjes <rientjes@google.com>
---
 mm/sparse.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index d882e88..51950de 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -130,6 +130,8 @@ int __section_nr(struct mem_section* ms)
 		     break;
 	}
 
+	VM_BUG_ON(root_nr == NR_SECTION_ROOTS);
+
 	return (root_nr * SECTIONS_PER_ROOT) + (ms - root);
 }
 
-- 
1.7.5.4

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Re: [PATCH RESEND v4 2/3] mm/sparse: more check on mem_section number

[Cong Wang]

On Mon, 23 Jul 2012 at 02:31 GMT, Gavin Shan <shangw@linux.vnet.ibm.com> wrote:
> Function __section_nr() was implemented to retrieve the corresponding
> memory section number according to its descriptor. It's possible that
> the specified memory section descriptor isn't existing in the global
> array. So here to add more check on that and report error for wrong
> case.
>
> Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
> Acked-by: David Rientjes <rientjes@google.com>

Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com>

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[PATCH RESEND v2 3/3] mm/sparse: remove index_init_lock

[Gavin Shan]

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.

[mhocko@suse.cz: changelog]
Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
---
 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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Re: [PATCH RESEND v2 3/3] mm/sparse: remove index_init_lock

[Cong Wang]

On Mon, 23 Jul 2012 at 02:31 GMT, Gavin Shan <shangw@linux.vnet.ibm.com> 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.
>
> [mhocko@suse.cz: changelog]
> Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
> Reviewed-by: Michal Hocko <mhocko@suse.cz>

Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com>

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Re: [PATCH RESEND v4 1/3] mm/sparse: optimize sparse_index_alloc

[Cong Wang]

On Mon, 23 Jul 2012 at 02:31 GMT, Gavin Shan <shangw@linux.vnet.ibm.com> wrote:
> With CONFIG_SPARSEMEM_EXTREME, the two level of memory section
> descriptors are allocated from slab or bootmem. When allocating
> from slab, let slab/bootmem allocator to clear the memory chunk.
> We needn't clear that explicitly.
>
> Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
> Reviewed-by: Michal Hocko <mhocko@suse.cz>
> Acked-by: David Rientjes <rientjes@google.com>

Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com>


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Re: [PATCH RESEND v4 1/3] mm/sparse: optimize sparse_index_alloc

[Gavin Shan]

On Mon, Jul 23, 2012 at 08:18:04AM +0000, Cong Wang wrote:
>On Mon, 23 Jul 2012 at 02:31 GMT, Gavin Shan <shangw@linux.vnet.ibm.com> wrote:
>> With CONFIG_SPARSEMEM_EXTREME, the two level of memory section
>> descriptors are allocated from slab or bootmem. When allocating
>> from slab, let slab/bootmem allocator to clear the memory chunk.
>> We needn't clear that explicitly.
>>
>> Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
>> Reviewed-by: Michal Hocko <mhocko@suse.cz>
>> Acked-by: David Rientjes <rientjes@google.com>
>
>Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com>
>

Thanks for your time, Cong :-)

Thanks,
Gavin

>
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Re: [PATCH RESEND v4 1/3] mm/sparse: optimize sparse_index_alloc

[Gavin Shan]

On Mon, Jul 23, 2012 at 08:18:04AM +0000, Cong Wang wrote:
>On Mon, 23 Jul 2012 at 02:31 GMT, Gavin Shan <shangw@linux.vnet.ibm.com> wrote:
>> With CONFIG_SPARSEMEM_EXTREME, the two level of memory section
>> descriptors are allocated from slab or bootmem. When allocating
>> from slab, let slab/bootmem allocator to clear the memory chunk.
>> We needn't clear that explicitly.
>>
>> Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
>> Reviewed-by: Michal Hocko <mhocko@suse.cz>
>> Acked-by: David Rientjes <rientjes@google.com>
>
>Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com>
>

Thanks for your time, Cong :-)

Thanks,
Gavin

>
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