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Date: Fri, 19 Jul 2019 10:48:19 +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 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?
I mean we can of course go ahead and drop the "NUMA_NO_NODE - 1" thingy
from the patch. A memory block with multiple nodes would (as of now)
only indicate one of the nodes.
Then there is simply no way to WARN_ON_ONCE() in case unexpected things
would happen. (I mean it really shouldn't happen or we have a BUG
somewhere else)
Alternative: Add "bool mixed_nids;" to "struct 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 | 40 ++++++++++++++++------------------------
>> include/linux/memory.h | 4 +++-
>> 3 files changed, 20 insertions(+), 25 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..29d27b8d5fda 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;
>> }
>> +
>> + /* this memory block spans this node */
>> + if (mem_blk->nid == NUMA_NO_NODE)
>> + mem_blk->nid = nid;
>> + else
>> + mem_blk->nid = NUMA_NO_NODE - 1;
>> +
>> ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
>> &mem_blk->dev.kobj,
>> kobject_name(&mem_blk->dev.kobj));
>> @@ -804,32 +809,19 @@ 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 ||
>> + WARN_ON_ONCE(mem_blk->nid == NUMA_NO_NODE - 1))
>> + 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)
>> diff --git a/include/linux/memory.h b/include/linux/memory.h
>> index 02e633f3ede0..c91af10d5fb4 100644
>> --- a/include/linux/memory.h
>> +++ b/include/linux/memory.h
>> @@ -33,7 +33,9 @@ struct memory_block {
>> void *hw; /* optional pointer to fw/hw data */
>> int (*phys_callback)(struct memory_block *);
>> struct device dev;
>> - int nid; /* NID for this memory block */
>> + int nid; /* NID for this memory block.
>> + - NUMA_NO_NODE: uninitialized
>> + - NUMA_NO_NODE - 1: mixed nodes */
>> };
>>
>> int arch_get_memory_phys_device(unsigned long start_pfn);
>> --
>> 2.21.0
>
--
Thanks,
David / dhildenb
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