[PATCH v3 0/4] misc patches related to resizing nodes & zones

[PATCH v3 0/4] misc patches related to resizing nodes & zones

[Cody P Schafer]

First 2 are comment fixes.
Second 2 add pgdat_resize_lock()/unlock() usage per existing documentation.

--

Since v2 (http://comments.gmane.org/gmane.linux.kernel.mm/99316):
 - add ack on patch 1 from rientjes.
 - quote documentation in patch 3 & 4.

--

Since v1 (http://thread.gmane.org/gmane.linux.kernel.mm/99297):
  - drop making lock_memory_hotplug() required (old patch #1)
  - fix __offline_pages() in the same manner as online_pages() (rientjes)
  - make comment regarding pgdat_resize_lock()/unlock() usage more clear (rientjes)


Cody P Schafer (4):
  mm: fix comment referring to non-existent size_seqlock, change to
    span_seqlock
  mmzone: note that node_size_lock should be manipulated via
    pgdat_resize_lock()
  memory_hotplug: use pgdat_resize_lock() in online_pages()
  memory_hotplug: use pgdat_resize_lock() in __offline_pages()

 include/linux/mmzone.h | 5 ++++-
 mm/memory_hotplug.c    | 9 +++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

-- 
1.8.2.2

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[PATCH v3 1/4] mm: fix comment referring to non-existent size_seqlock, change to span_seqlock

[Cody P Schafer]

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
Acked-by: David Rientjes <rientjes@google.com>
---
 include/linux/mmzone.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 5c76737..fc859a0c 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -716,7 +716,7 @@ typedef struct pglist_data {
 	 * or node_spanned_pages stay constant.  Holding this will also
 	 * guarantee that any pfn_valid() stays that way.
 	 *
-	 * Nests above zone->lock and zone->size_seqlock.
+	 * Nests above zone->lock and zone->span_seqlock
 	 */
 	spinlock_t node_size_lock;
 #endif
-- 
1.8.2.2

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[PATCH v3 2/4] mmzone: note that node_size_lock should be manipulated via pgdat_resize_lock()

[Cody P Schafer]

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
---
 include/linux/mmzone.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index fc859a0c..41557be 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -716,6 +716,9 @@ typedef struct pglist_data {
 	 * or node_spanned_pages stay constant.  Holding this will also
 	 * guarantee that any pfn_valid() stays that way.
 	 *
+	 * pgdat_resize_lock() and pgdat_resize_unlock() are provided to
+	 * manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG.
+	 *
 	 * Nests above zone->lock and zone->span_seqlock
 	 */
 	spinlock_t node_size_lock;
-- 
1.8.2.2

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[PATCH v3 3/4] memory_hotplug: use pgdat_resize_lock() in online_pages()

[Cody P Schafer]

mmzone.h documents node_size_lock (which pgdat_resize_lock() locks) as
follows:

        * Must be held any time you expect node_start_pfn, node_present_pages
        * or node_spanned_pages stay constant.  [...]

So actually hold it when we update node_present_pages in online_pages().

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
---
 mm/memory_hotplug.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index a221fac..0bdca10 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -915,6 +915,7 @@ static void node_states_set_node(int node, struct memory_notify *arg)
 
 int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_type)
 {
+	unsigned long flags;
 	unsigned long onlined_pages = 0;
 	struct zone *zone;
 	int need_zonelists_rebuild = 0;
@@ -993,7 +994,11 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
 
 	zone->managed_pages += onlined_pages;
 	zone->present_pages += onlined_pages;
+
+	pgdat_resize_lock(zone->zone_pgdat, &flags);
 	zone->zone_pgdat->node_present_pages += onlined_pages;
+	pgdat_resize_unlock(zone->zone_pgdat, &flags);
+
 	if (onlined_pages) {
 		node_states_set_node(zone_to_nid(zone), &arg);
 		if (need_zonelists_rebuild)
-- 
1.8.2.2

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Re: [PATCH v3 3/4] memory_hotplug: use pgdat_resize_lock() in online_pages()

[Andrew Morton]

On Mon, 13 May 2013 16:13:06 -0700 Cody P Schafer <cody@linux.vnet.ibm.com> wrote:

> mmzone.h documents node_size_lock (which pgdat_resize_lock() locks) as
> follows:
> 
>         * Must be held any time you expect node_start_pfn, node_present_pages
>         * or node_spanned_pages stay constant.  [...]

Yeah, I suppose so.  Although no present code sites actually do that.

> So actually hold it when we update node_present_pages in online_pages().
> 
> ...
>
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -915,6 +915,7 @@ static void node_states_set_node(int node, struct memory_notify *arg)
>  
>  int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_type)
>  {
> +	unsigned long flags;
>  	unsigned long onlined_pages = 0;
>  	struct zone *zone;
>  	int need_zonelists_rebuild = 0;
> @@ -993,7 +994,11 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
>  
>  	zone->managed_pages += onlined_pages;
>  	zone->present_pages += onlined_pages;
> +
> +	pgdat_resize_lock(zone->zone_pgdat, &flags);
>  	zone->zone_pgdat->node_present_pages += onlined_pages;
> +	pgdat_resize_unlock(zone->zone_pgdat, &flags);
> +
>  	if (onlined_pages) {
>  		node_states_set_node(zone_to_nid(zone), &arg);
>  		if (need_zonelists_rebuild)

afaict the only benefits of making this change are

a) so that code which does

	a = p->node_present_pages;
	...
	b = p->node_present_pages;

   can ensure that `a' and `b' are equal, by taking pgdat_resize_lock().

   Which is somewhat odd, and

b) to make the comment truthful ;)

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Re: [PATCH v3 3/4] memory_hotplug: use pgdat_resize_lock() in online_pages()

[David Rientjes]

On Wed, 15 May 2013, Andrew Morton wrote:

> On Mon, 13 May 2013 16:13:06 -0700 Cody P Schafer <cody@linux.vnet.ibm.com> wrote:
> 
> > mmzone.h documents node_size_lock (which pgdat_resize_lock() locks) as
> > follows:
> > 
> >         * Must be held any time you expect node_start_pfn, node_present_pages
> >         * or node_spanned_pages stay constant.  [...]
> 
> Yeah, I suppose so.  Although no present code sites actually do that.
> 

Agreed, I see no purpose in patches 2-4 in this series as mentioned in v2.

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[PATCH v3 4/4] memory_hotplug: use pgdat_resize_lock() in __offline_pages()

[Cody P Schafer]

mmzone.h documents node_size_lock (which pgdat_resize_lock() locks) as
follows:

        * Must be held any time you expect node_start_pfn, node_present_pages
        * or node_spanned_pages stay constant.  [...]

So actually hold it when we update node_present_pages in __offline_pages().

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
---
 mm/memory_hotplug.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 0bdca10..b59a695 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1582,7 +1582,11 @@ repeat:
 	/* removal success */
 	zone->managed_pages -= offlined_pages;
 	zone->present_pages -= offlined_pages;
+
+	pgdat_resize_lock(zone->zone_pgdat, &flags);
 	zone->zone_pgdat->node_present_pages -= offlined_pages;
+	pgdat_resize_unlock(zone->zone_pgdat, &flags);
+
 	totalram_pages -= offlined_pages;
 
 	init_per_zone_wmark_min();
-- 
1.8.2.2

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