Subject: Re: [RFC PATCH 4/12] memory-hotplug : remove /sys/firmware/memmap/X sysfs

From: Yasuaki Ishimatsu <[email-masked]>
Date: Thu, 28 Jun 2012 17:07:39 +0900

Hi Wen,

2012/06/28 15:32, Wen Congyang wrote:
> At 06/27/2012 01:47 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: Len Brown <[email-masked]>
>> CC: Benjamin Herrenschmidt <[email-masked]>
>> CC: Paul Mackerras <[email-masked]>
>> CC: Christoph Lameter <[email-masked]>
>> Cc: Minchan Kim <[email-masked]>
>> CC: Andrew Morton <[email-masked]>
>> CC: KOSAKI Motohiro <[email-masked]>
>> CC: Wen Congyang <[email-masked]>
>> Signed-off-by: Yasuaki Ishimatsu <[email-masked]>
>>
>> ---
>>   drivers/firmware/memmap.c    |   71 +++++++++++++++++++++++++++++++++++++++++++
>>   include/linux/firmware-map.h |    6 +++
>>   mm/memory_hotplug.c          |    6 +++
>>   3 files changed, 82 insertions(+), 1 deletion(-)
>>
>> Index: linux-3.5-rc4/mm/memory_hotplug.c
>> ===================================================================
>> --- linux-3.5-rc4.orig/mm/memory_hotplug.c	2012-06-26 13:37:30.546288901 +0900
>> +++ linux-3.5-rc4/mm/memory_hotplug.c	2012-06-26 13:44:37.069955820 +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, "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	2012-06-25 04:53:04.000000000 +0900
>> +++ linux-3.5-rc4/include/linux/firmware-map.h	2012-06-26 13:44:37.070955807 +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	2012-06-25 04:53:04.000000000 +0900
>> +++ linux-3.5-rc4/drivers/firmware/memmap.c	2012-06-26 13:47:17.606948898 +0900
>> @@ -123,6 +123,16 @@ static int firmware_map_add_entry(u64 st
>>   	return 0;
>>   }
>>
>> +/**
>> + * firmware_map_remove_entry() - Does the real work to remove a firmware
>> + * memmap entry.
>> + * @entry: removed entry.
>> + **/
>> +static inline void firmware_map_remove_entry(struct firmware_map_entry *entry)
>> +{
>> +	list_del(&entry->list);
>> +}
>> +
>>   /*
>>    * Add memmap entry on sysfs
>>    */
>> @@ -144,6 +154,31 @@ static int add_sysfs_fw_map_entry(struct
>>   	return 0;
>>   }
>>
>> +/*
>> + * Remove memmap entry on sysfs
>> + */
>> +static inline void remove_sysfs_fw_map_entry(struct firmware_map_entry *entry)
>> +{
>> +	kobject_del(&entry->kobj);
>> +}
>> +
>> +/*
>> + * Search memmap entry
>> + */
>> +
>> +struct firmware_map_entry * __meminit
>> +find_firmware_map_entry(u64 start, u64 end, const char *type)
>> +{
>> +	struct firmware_map_entry *entry;
>> +
>> +	list_for_each_entry(entry, &map_entries, list)
>> +		if ((entry->start == start) && (entry->end == end) &&
>> +		    (!strcmp(entry->type, type)))
>> +			return entry;
>> +
>> +	return NULL;
>> +}
>> +
>>   /**
>>    * firmware_map_add_hotplug() - Adds a firmware mapping entry when we do
>>    * memory hotplug.
>> @@ -196,6 +231,42 @@ int __init firmware_map_add_early(u64 st
>>   	return firmware_map_add_entry(start, end, type, entry);
>>   }
>>
>> +void release_firmware_map_entry(struct firmware_map_entry *entry)
>> +{
>> +	/*
>> +	 * FIXME : There is no idea.
>> +	 *         How to free the entry which allocated bootmem?
>> +	 */
>> +}
>> +
>> +/**
>> + * firmware_map_remove() - remove a firmware mapping entry
>> + * @start: Start of the memory range.
>> + * @end:   End of the memory range (inclusive).
>> + * @type:  Type of the memory range.
>> + *
>> + * removes a firmware mapping entry.
>> + *
>> + * Returns 0 on success, or -EINVAL if no entry.
>> + **/
>> +int __meminit firmware_map_remove(u64 start, u64 end, const char *type)
>> +{
>> +	struct firmware_map_entry *entry;
>> +
>> +	entry = find_firmware_map_entry(start, end, type);
>
> Hmm, we cannot find the entry easily, because the end can be:
> 1. start + size
> 2. start + size - 1
>
> So, We should fix this bug first.

This is not a bug.

start and size arguments of firmware_map_remove() include
acpi_memory_info->{start_addr, length}. And when creating a firmware_map_entry,
the entry is created by acpi_memory_info->{start_addr, length}. So I don't
think that we need care your comment.

>
>> +	if (!entry)
>> +		return -EINVAL;
>> +
>> +	/* remove the memmap entry */
>> +	remove_sysfs_fw_map_entry(entry);
>> +
>> +	firmware_map_remove_entry(entry);
>> +
>> +	release_firmware_map_entry(entry);
>
> I guess you want to free the memory in the above function. But I think it is
> not a good idea to free it here. We should free it when the entry->kobj's kref
> is decreased to 0.

Thanks.
I'll update your comment at next version.

Thanks,
Yasuaki Ishimatsu

>
> Thanks
> Wen Congyang
>
>> +
>> +	return 0;
>> +}
>> +
>>   /*
>>    * Sysfs functions -------------------------------------------------------------
>>    */
>>
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