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SubjectRe: [PATCH v1 05/12] mm/memory_hotplug: remove nid parameter from remove_memory() and friends
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On 08.06.21 13:18, David Hildenbrand wrote:
> On 08.06.21 13:11, Michael Ellerman wrote:
>> David Hildenbrand <david@redhat.com> writes:
>>> There is only a single user remaining. We can simply try to offline all
>>> online nodes - which is fast, because we usually span pages and can skip
>>> such nodes right away.
>>
>> That makes me slightly nervous, because our big powerpc boxes tend to
>> trip on these scaling issues before others.
>>
>> But the spanned pages check is just:
>>
>> void try_offline_node(int nid)
>> {
>> pg_data_t *pgdat = NODE_DATA(nid);
>> ...
>> if (pgdat->node_spanned_pages)
>> return;
>>
>> So I guess that's pretty cheap, and it's only O(nodes), which should
>> never get that big.
>
> Exactly. And if it does turn out to be a problem, we can walk all memory
> blocks before removing them, collecting the nid(s).
>

I might just do the following on top:

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 61bff8f3bfb1..bbc26fdac364 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -2176,7 +2176,9 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
static int check_memblock_offlined_cb(struct memory_block *mem, void *arg)
{
int ret = !is_memblock_offlined(mem);
+ int *nid = arg;

+ *nid = mem->nid;
if (unlikely(ret)) {
phys_addr_t beginpa, endpa;

@@ -2271,10 +2273,10 @@ EXPORT_SYMBOL(try_offline_node);

static int __ref try_remove_memory(u64 start, u64 size)
{
- int rc = 0, nid;
struct vmem_altmap mhp_altmap = {};
struct vmem_altmap *altmap = NULL;
unsigned long nr_vmemmap_pages;
+ int rc = 0, nid = NUMA_NO_NODE;

BUG_ON(check_hotplug_memory_range(start, size));

@@ -2282,8 +2284,12 @@ static int __ref try_remove_memory(u64 start, u64 size)
* All memory blocks must be offlined before removing memory. Check
* whether all memory blocks in question are offline and return error
* if this is not the case.
+ *
+ * While at it, determine the nid. Note that if we'd have mixed nodes,
+ * we'd only try to offline the last determined one -- which is good
+ * enough for the cases we care about.
*/
- rc = walk_memory_blocks(start, size, NULL, check_memblock_offlined_cb);
+ rc = walk_memory_blocks(start, size, &nid, check_memblock_offlined_cb);
if (rc)
return rc;

@@ -2332,7 +2338,7 @@ static int __ref try_remove_memory(u64 start, u64 size)

release_mem_region_adjustable(start, size);

- for_each_online_node(nid)
+ if (nid != NUMA_NO_NODE)
try_offline_node(nid);

mem_hotplug_done();


--
Thanks,

David / dhildenb

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