linux-kernel - [PATCH] fix updating of num_physpages for hot plugged memory

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Message-Id: <4A8AE5F50200007800010536@vpn.id2.novell.com>
Date:	Tue, 18 Aug 2009 16:33:41 +0100
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Cc:	"Rusty Russell" <rusty@...tcorp.com.au>
Subject: [PATCH] fix updating of num_physpages for hot plugged memory

Sizing of memory allocations shouldn't depend on the number of physical
pages found in a system, as that generally includes (perhaps a huge
amount of) non-RAM pages. The amount of what actually is usable as
storage should instead be used as a basis here.

In line with that, the memory hotplug code should update num_physpages
in a way that it retains its original (post-boot) meaning; in
particular, decreasing the value should at best be done with great care
- this patch doesn't try to ever decrease this value at all as it
doesn't really seem meaningful to do so.

Signed-off-by: Jan Beulich <jbeulich@...ell.com>
Acked-by: Rusty Russell <rusty@...tcorp.com.au>

---
 mm/memory_hotplug.c               |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- linux-2.6.31-rc6/mm/memory_hotplug.c	2009-08-18 15:31:56.000000000 +0200
+++ 2.6.31-rc6-use-totalram_pages/mm/memory_hotplug.c	2009-08-17 15:21:19.000000000 +0200
@@ -339,8 +339,11 @@ EXPORT_SYMBOL_GPL(__remove_pages);
 
 void online_page(struct page *page)
 {
+	unsigned long pfn = page_to_pfn(page);
+
 	totalram_pages++;
-	num_physpages++;
+	if (pfn >= num_physpages)
+		num_physpages = pfn + 1;
 
 #ifdef CONFIG_HIGHMEM
 	if (PageHighMem(page))
@@ -831,7 +834,6 @@ repeat:
 	zone->present_pages -= offlined_pages;
 	zone->zone_pgdat->node_present_pages -= offlined_pages;
 	totalram_pages -= offlined_pages;
-	num_physpages -= offlined_pages;
 
 	setup_per_zone_wmarks();
 	calculate_zone_inactive_ratio(zone);



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