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memory hotplug: Speed up add/remove when blocks are larger than PAGES_PER_SECTION

PATCH In review Anton Blanchard 3 participants 3 messages May 11, 2011

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Driver core Memory hot(un)plug
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Anton Blanchard

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#0 lore raw

PATCH 1/1 memory hotplug: Speed up add/remove when blocks are larger than PAGES_PER_SECTION

On ppc64 the minimum memory section for hotplug is 16MB but most recent machines have a memory block size of 256MB. This means memory_block_change_state does 16 separate calls to memory_section_action.

This also means we call the notifiers 16 times and the hook in the ehea network driver is quite costly. To offline one 256MB region takes:

# time echo offline > /sys/devices/system/memory/memory32/state
7.9s

This patch removes the loop and calls online_pages or remove_memory once for the entire region and in doing so makes the logic simpler since we don't have to back out if things fail part way through.

The same test to offline one region now takes:

# time echo online > /sys/devices/system/memory/memory32/state
0.67s

Over 11 times faster.

Signed-off-by Anton Blanchard <[email protected]>

---

drivers/base/memory.c +8 -16
Index: linux-2.6-work/drivers/base/memory.c
===================================================================
@@ -228,10 +228,11 @@ int memory_isolate_notify(unsigned long
  * OK to have direct references to sparsemem variables in here.
  */
 static int
-memory_section_action(unsigned long phys_index, unsigned long action)
+memory_block_action(unsigned long phys_index, unsigned long action)
 {
 	int i;
 	unsigned long start_pfn, start_paddr;
+	unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
 	struct page *first_page;
 	int ret;
 

@@ -243,7 +244,7 @@ memory_section_action(unsigned long phys
 	 * that way.
 	 */
 	if (action == MEM_ONLINE) {
-		for (i = 0; i < PAGES_PER_SECTION; i++) {
+		for (i = 0; i < nr_pages; i++) {
 			if (PageReserved(first_page+i))
 				continue;
 

@@ -257,12 +258,12 @@ memory_section_action(unsigned long phys
 	switch (action) {
 		case MEM_ONLINE:
 			start_pfn = page_to_pfn(first_page);
-			ret = online_pages(start_pfn, PAGES_PER_SECTION);
+			ret = online_pages(start_pfn, nr_pages);
 			break;
 		case MEM_OFFLINE:
 			start_paddr = page_to_pfn(first_page) << PAGE_SHIFT;
 			ret = remove_memory(start_paddr,
-					    PAGES_PER_SECTION << PAGE_SHIFT);
+					    nr_pages << PAGE_SHIFT);
 			break;
 		default:
 			WARN(1, KERN_WARNING "%s(%ld, %ld) unknown action: "

@@ -288,20 +289,11 @@ static int memory_block_change_state(str
 	if (to_state == MEM_OFFLINE)
 		mem->state = MEM_GOING_OFFLINE;
 
-	for (i = 0; i < sections_per_block; i++) {
-		ret = memory_section_action(mem->start_section_nr + i,
-					    to_state);
-		if (ret)
-			break;
-	}
-
-	if (ret) {
-		for (i = 0; i < sections_per_block; i++)
-			memory_section_action(mem->start_section_nr + i,
-					      from_state_req);
+	ret = memory_block_action(mem->start_section_nr, to_state);
 
+	if (ret)
 		mem->state = from_state_req;
-	} else
+	else
 		mem->state = to_state;
 
 out:
#1 lore raw
Quoted 18 lines · Anton Blanchard

On ppc64 the minimum memory section for hotplug is 16MB but most recent machines have a memory block size of 256MB. This means memory_block_change_state does 16 separate calls to memory_section_action.

This also means we call the notifiers 16 times and the hook in the ehea network driver is quite costly. To offline one 256MB region takes:

# time echo offline > /sys/devices/system/memory/memory32/state
7.9s

This patch removes the loop and calls online_pages or remove_memory once for the entire region and in doing so makes the logic simpler since we don't have to back out if things fail part way through.

Quoted 6 lines

The same test to offline one region now takes:

# time echo online > /sys/devices/system/memory/memory32/state
0.67s

Over 11 times faster.

Very nice job, I'll queue this up for .40.

thanks,

greg k-h

#2 lore raw
In reply to Anton Blanchard
Quoted 18 lines · Anton Blanchard

On ppc64 the minimum memory section for hotplug is 16MB but most recent machines have a memory block size of 256MB. This means memory_block_change_state does 16 separate calls to memory_section_action.

This also means we call the notifiers 16 times and the hook in the ehea network driver is quite costly. To offline one 256MB region takes:

# time echo offline > /sys/devices/system/memory/memory32/state
7.9s

This patch removes the loop and calls online_pages or remove_memory once for the entire region and in doing so makes the logic simpler since we don't have to back out if things fail part way through.

Quoted 8 lines

The same test to offline one region now takes:

# time echo online > /sys/devices/system/memory/memory32/state
0.67s

Over 11 times faster.

Signed-off-by Anton Blanchard <[email protected]>

Your patch introduced a compiler warning, care to send a follow-on patch fixing this up:
drivers/base/memory.c: In function ‘memory_block_change_state’:
drivers/base/memory.c:281:6: warning: unused variable ‘i’

thanks,

greg k-h