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SubjectRe: [PATCH v5 01/14] memory-hotplug: try to offline the memory twice to avoid dependence
At 12/26/2012 11:02 AM, Kamezawa Hiroyuki Wrote:
> (2012/12/24 21:09), Tang Chen wrote:
>> From: Wen Congyang <wency@cn.fujitsu.com>
>>
>> memory can't be offlined when CONFIG_MEMCG is selected.
>> For example: there is a memory device on node 1. The address range
>> is [1G, 1.5G). You will find 4 new directories memory8, memory9, memory10,
>> and memory11 under the directory /sys/devices/system/memory/.
>>
>> If CONFIG_MEMCG is selected, we will allocate memory to store page cgroup
>> when we online pages. When we online memory8, the memory stored page cgroup
>> is not provided by this memory device. But when we online memory9, the memory
>> stored page cgroup may be provided by memory8. So we can't offline memory8
>> now. We should offline the memory in the reversed order.
>>
>
> If memory8 is onlined as NORMAL memory ...right ?

Yes, memory8 is onlined as NORMAL memory. And when we online memory9, we allocate
memory from memory8 to store page cgroup information.

>
> IIUC, vmalloc() uses __GFP_HIGHMEM but doesn't use __GFP_MOVABLE.
>
>> When the memory device is hotremoved, we will auto offline memory provided
>> by this memory device. But we don't know which memory is onlined first, so
>> offlining memory may fail. In such case, iterate twice to offline the memory.
>> 1st iterate: offline every non primary memory block.
>> 2nd iterate: offline primary (i.e. first added) memory block.
>>
>> This idea is suggested by KOSAKI Motohiro.
>>
>> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
>
> I'm not sure but the whole DIMM should be onlined as MOVABLE mem ?

If the whole DIMM is onlined as MOVABLE mem, we can offline it, and don't
retry again.

>
> Anyway, I agree this kind of retry is required if memory is onlined as NORMAL mem.
> But retry-once is ok ?

I'am not sure, but I think in most cases the user may online the memory according first
which is hot-added first. So we may always fail in the first time, and retry-once can
success.

Thanks
Wen Congyang

>
> Thanks,
> -Kame
>
>> ---
>> mm/memory_hotplug.c | 16 ++++++++++++++--
>> 1 files changed, 14 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index d04ed87..62e04c9 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1388,10 +1388,13 @@ int remove_memory(u64 start, u64 size)
>> unsigned long start_pfn, end_pfn;
>> unsigned long pfn, section_nr;
>> int ret;
>> + int return_on_error = 0;
>> + int retry = 0;
>>
>> start_pfn = PFN_DOWN(start);
>> end_pfn = start_pfn + PFN_DOWN(size);
>>
>> +repeat:
>> for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
>> section_nr = pfn_to_section_nr(pfn);
>> if (!present_section_nr(section_nr))
>> @@ -1410,14 +1413,23 @@ int remove_memory(u64 start, u64 size)
>>
>> ret = offline_memory_block(mem);
>> if (ret) {
>> - kobject_put(&mem->dev.kobj);
>> - return ret;
>> + if (return_on_error) {
>> + kobject_put(&mem->dev.kobj);
>> + return ret;
>> + } else {
>> + retry = 1;
>> + }
>> }
>> }
>>
>> if (mem)
>> kobject_put(&mem->dev.kobj);
>>
>> + if (retry) {
>> + return_on_error = 1;
>> + goto repeat;
>> + }
>> +
>> return 0;
>> }
>> #else
>>
>
>
>



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