linux-kernel - [patch -mm] mm: slab allocate memory section nodemask for large systems

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Date:	Wed, 28 Oct 2009 13:43:42 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Gary Hade <garyhade@...ibm.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Badari Pulavarty <pbadari@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>, Alex Chiang <achiang@...com>
Subject: [patch -mm] mm: slab allocate memory section nodemask for large
 systems

On Wed, 28 Oct 2009, Alex Chiang wrote:

> Am I not understanding the code? It looks like we do this
> already...
> 
> /* unregister memory section under all nodes that it spans */
> int unregister_mem_sect_under_nodes(struct memory_block *mem_blk)
> {
> 	nodemask_t unlinked_nodes;
> 	unsigned long pfn, sect_start_pfn, sect_end_pfn;
> 
> 	if (!mem_blk)
> 		return -EFAULT;
> 	nodes_clear(unlinked_nodes);
> 	sect_start_pfn = section_nr_to_pfn(mem_blk->phys_index);
> 	sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1;
> 	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
> 		int nid;
> 
> 		nid = get_nid_for_pfn(pfn);
> 		if (nid < 0)
> 			continue;
> 		if (!node_online(nid))
> 			continue;
> 		if (node_test_and_set(nid, unlinked_nodes))
> 			continue;
> 		sysfs_remove_link(&node_devices[nid].sysdev.kobj,
> 			 kobject_name(&mem_blk->sysdev.kobj));
> 		sysfs_remove_link(&mem_blk->sysdev.kobj,
> 			 kobject_name(&node_devices[nid].sysdev.kobj));
> 	}
> 	return 0;
> }
> 

That shound be sufficient with the exception that allocating nodemask_t 
on the stack is usually dangerous because it can be extremely large; we 
typically use NODEMASK_ALLOC() for such code.  It's had some changes in 
-mm, but since this patchset will likely be going through that tree anyway 
we can fix it now with the patch below.

Otherwise, it looks like the iteration is already there and will remove 
links for memory sections bound to multiple nodes if they exist through 
hotplug.



mm: slab allocate memory section nodemask for large systems

Nodemasks should not be allocated on the stack for large systems (when it
is larger than 256 bytes) since there is a threat of overflow.

This patch causes the unregister_mem_sect_under_nodes() nodemask to be
allocated on the stack for smaller systems and be allocated by slab for
larger systems.

GFP_KERNEL is used since remove_memory_block() can block.

Cc: Gary Hade <garyhade@...ibm.com>
Cc: Badari Pulavarty <pbadari@...ibm.com>
Signed-off-by: David Rientjes <rientjes@...gle.com>
---
 Depends on NODEMASK_ALLOC() changes currently present only in -mm.

 drivers/base/node.c |   11 +++++++----
 1 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -363,12 +363,14 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, int nid)
 /* unregister memory section under all nodes that it spans */
 int unregister_mem_sect_under_nodes(struct memory_block *mem_blk)
 {
-	nodemask_t unlinked_nodes;
+	NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL);
 	unsigned long pfn, sect_start_pfn, sect_end_pfn;
 
-	if (!mem_blk)
+	if (!mem_blk) {
+		NODEMASK_FREE(unlinked_nodes);
 		return -EFAULT;
-	nodes_clear(unlinked_nodes);
+	}
+	nodes_clear(*unlinked_nodes);
 	sect_start_pfn = section_nr_to_pfn(mem_blk->phys_index);
 	sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1;
 	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
@@ -379,13 +381,14 @@ int unregister_mem_sect_under_nodes(struct memory_block *mem_blk)
 			continue;
 		if (!node_online(nid))
 			continue;
-		if (node_test_and_set(nid, unlinked_nodes))
+		if (node_test_and_set(nid, *unlinked_nodes))
 			continue;
 		sysfs_remove_link(&node_devices[nid].sysdev.kobj,
 			 kobject_name(&mem_blk->sysdev.kobj));
 		sysfs_remove_link(&mem_blk->sysdev.kobj,
 			 kobject_name(&node_devices[nid].sysdev.kobj));
 	}
+	NODEMASK_FREE(unlinked_nodes);
 	return 0;
 }
 
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