Subject: Re: [PATCH v5 01/14] memory-hotplug: try to offline the memory twice to avoid dependence

From: Kamezawa Hiroyuki <[email-masked]>
Date: Wed, 26 Dec 2012 12:02:00 +0900

(2012/12/24 21:09), Tang Chen wrote:
> From: Wen Congyang <[email-masked]>
> 
> 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 ?

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 <[email-masked]>

I'm not sure but the whole DIMM should be onlined as MOVABLE mem ?

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

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
>