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Date: Fri, 19 Jul 2019 11:20:43 +0200
From: David Hildenbrand <david@...hat.com>
To: Michal Hocko <mhocko@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Stephen Rothwell <sfr@...b.auug.org.au>,
Pavel Tatashin <pasha.tatashin@...een.com>,
Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v1] drivers/base/node.c: Simplify
unregister_memory_block_under_nodes()
On 19.07.19 11:13, Michal Hocko wrote:
> On Fri 19-07-19 11:05:51, David Hildenbrand wrote:
>> On 19.07.19 10:42, Michal Hocko wrote:
>>> On Thu 18-07-19 16:22:39, David Hildenbrand wrote:
>>>> We don't allow to offline memory block devices that belong to multiple
>>>> numa nodes. Therefore, such devices can never get removed. It is
>>>> sufficient to process a single node when removing the memory block.
>>>>
>>>> Remember for each memory block if it belongs to no, a single, or mixed
>>>> nodes, so we can use that information to skip unregistering or print a
>>>> warning (essentially a safety net to catch BUGs).
>>>
>>> I do not really like NUMA_NO_NODE - 1 thing. This is yet another invalid
>>> node that is magic. Why should we even care? In other words why is this
>>> patch an improvement?
>>
>> Oh, and to answer that part of the question:
>>
>> We no longer have to iterate over each pfn of a memory block to be removed.
>
> Is it possible that we are overzealous when unregistering syfs files and
> we should simply skip the pfn walk even without this change?
>
I assume you mean something like v1 without the warning/"NUMA_NO_NODE -1"?
See what I have right now below.
>From 27e9b02146e5fbe8edac49767693fa18c9b204dd Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@...hat.com>
Date: Thu, 18 Jul 2019 15:48:41 +0200
Subject: [PATCH v2] drivers/base/node.c: Simplify
unregister_memory_block_under_nodes()
We don't allow to offline memory block devices that belong to multiple
numa nodes. Therefore, such devices can never get removed. It is
sufficient to process a single node when removing the memory block.
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>
Cc: Stephen Rothwell <sfr@...b.auug.org.au>
Cc: Pavel Tatashin <pasha.tatashin@...een.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Oscar Salvador <osalvador@...e.de>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
drivers/base/memory.c | 1 +
drivers/base/node.c | 39 +++++++++++++++------------------------
2 files changed, 16 insertions(+), 24 deletions(-)
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 20c39d1bcef8..154d5d4a0779 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -674,6 +674,7 @@ static int init_memory_block(struct memory_block **memory,
mem->state = state;
start_pfn = section_nr_to_pfn(mem->start_section_nr);
mem->phys_device = arch_get_memory_phys_device(start_pfn);
+ mem->nid = NUMA_NO_NODE;
ret = register_memory(mem);
diff --git a/drivers/base/node.c b/drivers/base/node.c
index 75b7e6f6535b..840c95baa1d8 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -759,8 +759,6 @@ static int register_mem_sect_under_node(struct memory_block *mem_blk,
int ret, nid = *(int *)arg;
unsigned long pfn, sect_start_pfn, sect_end_pfn;
- mem_blk->nid = nid;
-
sect_start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
sect_end_pfn += PAGES_PER_SECTION - 1;
@@ -789,6 +787,13 @@ static int register_mem_sect_under_node(struct memory_block *mem_blk,
if (page_nid != nid)
continue;
}
+
+ /*
+ * If this memory block spans multiple nodes, we only indicate
+ * the last processed node.
+ */
+ mem_blk->nid = nid;
+
ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
&mem_blk->dev.kobj,
kobject_name(&mem_blk->dev.kobj));
@@ -804,32 +809,18 @@ static int register_mem_sect_under_node(struct memory_block *mem_blk,
}
/*
- * Unregister memory block device under all nodes that it spans.
- * Has to be called with mem_sysfs_mutex held (due to unlinked_nodes).
+ * Unregister a memory block device under the node it spans. Memory blocks
+ * with multiple nodes cannot be offlined and therefore also never be removed.
*/
void unregister_memory_block_under_nodes(struct memory_block *mem_blk)
{
- unsigned long pfn, sect_start_pfn, sect_end_pfn;
- static nodemask_t unlinked_nodes;
-
- nodes_clear(unlinked_nodes);
- sect_start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
- sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
- for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
- int nid;
+ if (mem_blk->nid == NUMA_NO_NODE)
+ return;
- 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]->dev.kobj,
- kobject_name(&mem_blk->dev.kobj));
- sysfs_remove_link(&mem_blk->dev.kobj,
- kobject_name(&node_devices[nid]->dev.kobj));
- }
+ sysfs_remove_link(&node_devices[mem_blk->nid]->dev.kobj,
+ kobject_name(&mem_blk->dev.kobj));
+ sysfs_remove_link(&mem_blk->dev.kobj,
+ kobject_name(&node_devices[mem_blk->nid]->dev.kobj));
}
int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn)
--
2.21.0
--
Thanks,
David / dhildenb
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