Re: [Patch v4 01/12] memory-hotplug: try to offline the memory twice to avoid dependence

Tang Chen
2012-12-04T09:17:30Z

On 11/27/2012 06:00 PM, Wen Congyang wrote:
> 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.
>
> 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.
>
> CC: David Rientjes<rientjes@google.com>
> CC: Jiang Liu<liuj97@gmail.com>
> CC: Len Brown<len.brown@intel.com>
> CC: Christoph Lameter<cl@linux.com>
> Cc: Minchan Kim<minchan.kim@gmail.com>
> CC: Andrew Morton<akpm@linux-foundation.org>
> CC: KOSAKI Motohiro<kosaki.motohiro@jp.fujitsu.com>
> CC: Yasuaki Ishimatsu<isimatu.yasuaki@jp.fujitsu.com>
> Signed-off-by: Wen Congyang<wency@cn.fujitsu.com>

Reviewed-by: Tang Chen <tangchen@cn.fujitsu.com>

> ---
> mm/memory_hotplug.c | 16 ++++++++++++++--
> 1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index e4eeaca..b825dbc 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1012,10 +1012,13 @@ 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))
> @@ -1034,14 +1037,23 @@ 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