Re: [RFC PATCH v2 4/13] memory-hotplug : remove /sys/firmware/memmap/X sysfs

Yasuaki Ishimatsu
2012-07-09T08:19:14Z

Hi Wen,

2012/07/06 18:20, Wen Congyang wrote:
> At 07/06/2012 04:27 PM, Yasuaki Ishimatsu Wrote:
>> Hi Wen,
>>
>> 2012/07/04 19:01, Wen Congyang wrote:
>>> At 07/04/2012 01:52 PM, Yasuaki Ishimatsu Wrote:
>>>> Hi Wen,
>>>>
>>>> 2012/07/04 14:08, Wen Congyang wrote:
>>>>> At 07/04/2012 12:45 PM, Yasuaki Ishimatsu Wrote:
>>>>>> Hi Wen,
>>>>>>
>>>>>> 2012/07/03 15:35, Wen Congyang wrote:
>>>>>>> At 07/03/2012 01:56 PM, Yasuaki Ishimatsu Wrote:
>>>>>>>> When (hot)adding memory into system, /sys/firmware/memmap/X/{end, start, type}
>>>>>>>> sysfs files are created. But there is no code to remove these files. The patch
>>>>>>>> implements the function to remove them.
>>>>>>>>
>>>>>>>> Note : The code does not free firmware_map_entry since there is no way to free
>>>>>>>> memory which is allocated by bootmem.
>>>>>>>>
>>>>>>>> CC: David Rientjes <rientjes@google.com>
>>>>>>>> CC: Jiang Liu <liuj97@gmail.com>
>>>>>>>> CC: Len Brown <len.brown@intel.com>
>>>>>>>> CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>>>>>>>> CC: Paul Mackerras <paulus@samba.org>
>>>>>>>> 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: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
>>>>>>>>
>>>>>>>> ---
>>>>>>>> drivers/firmware/memmap.c | 70 +++++++++++++++++++++++++++++++++++++++++++
>>>>>>>> include/linux/firmware-map.h | 6 +++
>>>>>>>> mm/memory_hotplug.c | 6 +++
>>>>>>>> 3 files changed, 81 insertions(+), 1 deletion(-)
>>>>>>>>
>>>>>>>> Index: linux-3.5-rc4/mm/memory_hotplug.c
>>>>>>>> ===================================================================
>>>>>>>> --- linux-3.5-rc4.orig/mm/memory_hotplug.c 2012-07-03 14:22:00.190240794 +0900
>>>>>>>> +++ linux-3.5-rc4/mm/memory_hotplug.c 2012-07-03 14:22:03.549198802 +0900
>>>>>>>> @@ -661,7 +661,11 @@ EXPORT_SYMBOL_GPL(add_memory);
>>>>>>>>
>>>>>>>> int remove_memory(int nid, u64 start, u64 size)
>>>>>>>> {
>>>>>>>> - return -EBUSY;
>>>>>>>> + lock_memory_hotplug();
>>>>>>>> + /* remove memmap entry */
>>>>>>>> + firmware_map_remove(start, start + size - 1, "System RAM");
>>>>>>>> + unlock_memory_hotplug();
>>>>>>>> + return 0;
>>>>>>>>
>>>>>>>> }
>>>>>>>> EXPORT_SYMBOL_GPL(remove_memory);
>>>>>>>> Index: linux-3.5-rc4/include/linux/firmware-map.h
>>>>>>>> ===================================================================
>>>>>>>> --- linux-3.5-rc4.orig/include/linux/firmware-map.h 2012-07-03 14:21:45.766421116 +0900
>>>>>>>> +++ linux-3.5-rc4/include/linux/firmware-map.h 2012-07-03 14:22:03.550198789 +0900
>>>>>>>> @@ -25,6 +25,7 @@
>>>>>>>>
>>>>>>>> int firmware_map_add_early(u64 start, u64 end, const char *type);
>>>>>>>> int firmware_map_add_hotplug(u64 start, u64 end, const char *type);
>>>>>>>> +int firmware_map_remove(u64 start, u64 end, const char *type);
>>>>>>>>
>>>>>>>> #else /* CONFIG_FIRMWARE_MEMMAP */
>>>>>>>>
>>>>>>>> @@ -38,6 +39,11 @@ static inline int firmware_map_add_hotpl
>>>>>>>> return 0;
>>>>>>>> }
>>>>>>>>
>>>>>>>> +static inline int firmware_map_remove(u64 start, u64 end, const char *type)
>>>>>>>> +{
>>>>>>>> + return 0;
>>>>>>>> +}
>>>>>>>> +
>>>>>>>> #endif /* CONFIG_FIRMWARE_MEMMAP */
>>>>>>>>
>>>>>>>> #endif /* _LINUX_FIRMWARE_MAP_H */
>>>>>>>> Index: linux-3.5-rc4/drivers/firmware/memmap.c
>>>>>>>> ===================================================================
>>>>>>>> --- linux-3.5-rc4.orig/drivers/firmware/memmap.c 2012-07-03 14:21:45.761421180 +0900
>>>>>>>> +++ linux-3.5-rc4/drivers/firmware/memmap.c 2012-07-03 14:22:03.569198549 +0900
>>>>>>>> @@ -79,7 +79,16 @@ static const struct sysfs_ops memmap_att
>>>>>>>> .show = memmap_attr_show,
>>>>>>>> };
>>>>>>>>
>>>>>>>> +static void release_firmware_map_entry(struct kobject *kobj)
>>>>>>>> +{
>>>>>>>> + /*
>>>>>>>> + * FIXME : There is no idea.
>>>>>>>> + * How to free the entry which allocated bootmem?
>>>>>>>> + */
>>>>>>>
>>>>>>> I find a function free_bootmem(), but I am not sure whether it can work here.
>>>>>>
>>>>>> It cannot work here.
>>>>>>
>>>>>>> Another problem: how to check whether the entry uses bootmem?
>>>>>>
>>>>>> When firmware_map_entry is allocated by kzalloc(), the page has PG_slab.
>>>>>
>>>>> This is not true. In my test, I find the page does not have PG_slab sometimes.
>>>>
>>>> I think that it depends on the allocated size. firmware_map_entry size is
>>>> smaller than PAGE_SIZE. So the page has PG_Slab.
>>>
>>> In my test, I add printk in the function firmware_map_add_hotplug() to display
>>> page's flags. And sometimes the page is not allocated by slab(I use PageSlab()
>>> to verify it).
>>
>> How did you check it? Could you send your debug patch?
>
> When the memory is not allocated from slab, the flags is 0x10000000008000.

Thank you for sending the patch.
I think the page to not have PageSlab is a compound page. So we can check
whether the entry is allocate from bootmem or not as follow:

static void release_firmware_map_entry(struct kobject *kobj)
{
struct firmware_map_entry *entry = to_memmap_entry(kobj);
struct page *head_page;

head_page = virt_to_head_page(entry);
if (PageSlab(head_page))
kfree(etnry);
else
/* the entry is allocated from bootmem */
}

Thanks,
Yasuaki Ishimatsu

>
> From 8dd51368d6c03edf7edc89cab17441e3741c39c7 Mon Sep 17 00:00:00 2001
> From: Wen Congyang <wency@cn.fujitsu.com>
> Date: Wed, 4 Jul 2012 16:05:26 +0800
> Subject: [PATCH] debug
>
> ---
> drivers/firmware/memmap.c | 7 +++++++
> 1 files changed, 7 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/firmware/memmap.c b/drivers/firmware/memmap.c
> index adc0710..993ba3f 100644
> --- a/drivers/firmware/memmap.c
> +++ b/drivers/firmware/memmap.c
> @@ -21,6 +21,7 @@
> #include <linux/types.h>
> #include <linux/bootmem.h>
> #include <linux/slab.h>
> +#include <linux/mm.h>
>
> /*
> * Data types ------------------------------------------------------------------
> @@ -160,11 +161,17 @@ static int add_sysfs_fw_map_entry(struct firmware_map_entry *entry)
> int __meminit firmware_map_add_hotplug(u64 start, u64 end, const char *type)
> {
> struct firmware_map_entry *entry;
> + struct page *entry_page;
>
> entry = kzalloc(sizeof(struct firmware_map_entry), GFP_ATOMIC);
> if (!entry)
> return -ENOMEM;
>
> + entry_page = virt_to_page(entry);
> + printk(KERN_WARNING "flags: %lx\n", entry_page->flags);
> + if (PageSlab(entry_page)) {
> + printk(KERN_WARNING "page is allocated from slab\n");
> + }
> firmware_map_add_entry(start, end, type, entry);
> /* create the memmap entry */
> add_sysfs_fw_map_entry(entry);
>