Re: [PATCH 1/10] memory-hotplug : check whether memory is offline or not when removing memory

KOSAKI Motohiro
2012-10-05T19:27:47Z

On Thu, Oct 4, 2012 at 10:25 PM, Yasuaki Ishimatsu
<isimatu.yasuaki@jp.fujitsu.com> wrote:
> When calling remove_memory(), the memory should be offline. If the function
> is used to online memory, kernel panic may occur.
>
> So the patch checks whether memory is offline or not.

You don't explain WHY we need the check.

> 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>
> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
>
> ---
> drivers/base/memory.c | 39 +++++++++++++++++++++++++++++++++++++++
> include/linux/memory.h | 5 +++++
> mm/memory_hotplug.c | 17 +++++++++++++++--
> 3 files changed, 59 insertions(+), 2 deletions(-)
>
> Index: linux-3.6/drivers/base/memory.c
> ===================================================================
> --- linux-3.6.orig/drivers/base/memory.c 2012-10-04 14:22:57.000000000 +0900
> +++ linux-3.6/drivers/base/memory.c 2012-10-04 14:45:46.653585860 +0900
> @@ -70,6 +70,45 @@ void unregister_memory_isolate_notifier(
> }
> EXPORT_SYMBOL(unregister_memory_isolate_notifier);
>
> +bool is_memblk_offline(unsigned long start, unsigned long size)

Don't use memblk. Usually memblk mean struct numa_meminfo for x86/numa.
Maybe memory_range_offlined() is better.

And, this function don't take struct memory_block, then this file may be no good
place.

And you need to write down function comment.

> +{
> + struct memory_block *mem = NULL;
> + struct mem_section *section;
> + unsigned long start_pfn, end_pfn;
> + unsigned long pfn, section_nr;
> +
> + start_pfn = PFN_DOWN(start);
> + end_pfn = PFN_UP(start + size);
> +
> + for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
> + section_nr = pfn_to_section_nr(pfn);
> + if (!present_section_nr(section_nr))
> + continue;
> +
> + section = __nr_to_section(section_nr);
> + /* same memblock? */
> + if (mem)
> + if ((section_nr >= mem->start_section_nr) &&
> + (section_nr <= mem->end_section_nr))
> + continue;
> +
> + mem = find_memory_block_hinted(section, mem);
> + if (!mem)
> + continue;
> + if (mem->state == MEM_OFFLINE)
> + continue;
> +
> + kobject_put(&mem->dev.kobj);
> + return false;
> + }
> +
> + if (mem)
> + kobject_put(&mem->dev.kobj);
> +
> + return true;
> +}
> +EXPORT_SYMBOL(is_memblk_offline);
> +
> /*
> * register_memory - Setup a sysfs device for a memory block
> */
> Index: linux-3.6/include/linux/memory.h
> ===================================================================
> --- linux-3.6.orig/include/linux/memory.h 2012-10-02 18:00:22.000000000 +0900
> +++ linux-3.6/include/linux/memory.h 2012-10-04 14:44:40.902581028 +0900
> @@ -106,6 +106,10 @@ static inline int memory_isolate_notify(
> {
> return 0;
> }
> +static inline bool is_memblk_offline(unsigned long start, unsigned long size)
> +{
> + return false;
> +}
> #else
> extern int register_memory_notifier(struct notifier_block *nb);
> extern void unregister_memory_notifier(struct notifier_block *nb);
> @@ -120,6 +124,7 @@ extern int memory_isolate_notify(unsigne
> extern struct memory_block *find_memory_block_hinted(struct mem_section *,
> struct memory_block *);
> extern struct memory_block *find_memory_block(struct mem_section *);
> +extern bool is_memblk_offline(unsigned long start, unsigned long size);
> #define CONFIG_MEM_BLOCK_SIZE (PAGES_PER_SECTION<<PAGE_SHIFT)
> enum mem_add_context { BOOT, HOTPLUG };
> #endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
> Index: linux-3.6/mm/memory_hotplug.c
> ===================================================================
> --- linux-3.6.orig/mm/memory_hotplug.c 2012-10-04 14:31:08.000000000 +0900
> +++ linux-3.6/mm/memory_hotplug.c 2012-10-04 14:58:22.449687986 +0900
> @@ -1045,8 +1045,21 @@ int offline_memory(u64 start, u64 size)
>
> int remove_memory(int nid, u64 start, u64 size)
> {

Your remove_memory() don't remove anything. that's strange.

> - /* It is not implemented yet*/
> - return 0;
> + int ret = 0;
> + lock_memory_hotplug();
> + /*
> + * The memory might become online by other task, even if you offine it.
> + * So we check whether the memory has been onlined or not.
> + */
> + if (!is_memblk_offline(start, size)) {
> + pr_warn("memory removing [mem %#010llx-%#010llx] failed, "
> + "because the memmory range is online\n",
> + start, start + size);

No good warning. You should output which memory block can't be
offlined, I think.

> + ret = -EAGAIN;
> + }
> +
> + unlock_memory_hotplug();
> + return ret;
> }
> EXPORT_SYMBOL_GPL(remove_memory);
> #else
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: email@kvack.org