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Message-ID: <5044454E.7070909@cn.fujitsu.com>
Date: Mon, 03 Sep 2012 13:51:10 +0800
From: Wen Congyang <wency@...fujitsu.com>
To: Andrew Morton <akpm@...ux-foundation.org>
CC: x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
linux-ia64@...r.kernel.org, cmetcalf@...era.com,
sparclinux@...r.kernel.org, rientjes@...gle.com, liuj97@...il.com,
len.brown@...el.com, benh@...nel.crashing.org, paulus@...ba.org,
cl@...ux.com, minchan.kim@...il.com,
kosaki.motohiro@...fujitsu.com, isimatu.yasuaki@...fujitsu.com
Subject: Re: [RFC v8 PATCH 08/20] memory-hotplug: remove /sys/firmware/memmap/X
sysfs
At 09/01/2012 05:06 AM, Andrew Morton Wrote:
> On Tue, 28 Aug 2012 18:00:15 +0800
> wency@...fujitsu.com wrote:
>
>> From: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
>>
>> 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.
>>
>> ....
>>
>> +#define to_memmap_entry(obj) container_of(obj, struct firmware_map_entry, kobj)
>
> It would be better to implement this as an inlined C function. That
> has improved type safety and improved readability.
>
>> +static void release_firmware_map_entry(struct kobject *kobj)
>> +{
>> + struct firmware_map_entry *entry = to_memmap_entry(kobj);
>> + struct page *page;
>> +
>> + page = virt_to_page(entry);
>> + if (PageSlab(page) || PageCompound(page))
>
> That PageCompound() test looks rather odd. Why is this done?
Liu Jiang and Christoph Lameter discussed how to find slab page
in this mail:
https://lkml.org/lkml/2012/7/6/333.
>
>> + kfree(entry);
>> +
>> + /* There is no way to free memory allocated from bootmem*/
>> +}
>
> This function is a bit ugly - poking around in page flags to determine
> whether or not the memory came from bootmem. It would be cleaner to
> use a separate boolean. Although I guess we can live with it as you
> have it here.
>
>> static struct kobj_type memmap_ktype = {
>> + .release = release_firmware_map_entry,
>> .sysfs_ops = &memmap_attr_ops,
>> .default_attrs = def_attrs,
>> };
>> @@ -123,6 +139,16 @@ static int firmware_map_add_entry(u64 start, u64 end,
>> 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);
>> +}
>
> Is there no locking to protect that list?
>
>> /*
>> * Add memmap entry on sysfs
>> */
>> @@ -144,6 +170,31 @@ static int add_sysfs_fw_map_entry(struct firmware_map_entry *entry)
>> return 0;
>> }
>>
>> +/*
>> + * Remove memmap entry on sysfs
>> + */
>> +static inline void remove_sysfs_fw_map_entry(struct firmware_map_entry *entry)
>> +{
>> + kobject_put(&entry->kobj);
>> +}
>> +
>> +/*
>> + * Search memmap entry
>> + */
>> +
>> +struct firmware_map_entry * __meminit
>> +find_firmware_map_entry(u64 start, u64 end, const char *type)
>
> A better name would be firmware_map_find_entry(). To retain the (good)
> convention that symbols exported from here all start with
> "firmware_map_".
OK.
>
>> +{
>> + 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 +247,32 @@ int __init firmware_map_add_early(u64 start, u64 end, const char *type)
>> return firmware_map_add_entry(start, end, type, entry);
>> }
>>
>> +/**
>> + * firmware_map_remove() - remove a firmware mapping entry
>> + * @start: Start of the memory range.
>> + * @end: End of the memory range.
>> + * @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 - 1, type);
>> + if (!entry)
>> + return -EINVAL;
>> +
>> + firmware_map_remove_entry(entry);
>> +
>> + /* remove the memmap entry */
>> + remove_sysfs_fw_map_entry(entry);
>> +
>> + return 0;
>> +}
>
> Again, the lack of locking looks bad.
>
>> ...
>>
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1052,9 +1052,9 @@ int offline_memory(u64 start, u64 size)
>> return 0;
>> }
>>
>> -int remove_memory(int nid, u64 start, u64 size)
>> +int __ref remove_memory(int nid, u64 start, u64 size)
>
> Why was __ref added?
Hmm, firmware_map_remove() was put in meminit section, and we call it
in this function, so __ref is added here.
Thanks
Wen Congyang
>
>> {
>> - int ret = -EBUSY;
>> + int ret = 0;
>> lock_memory_hotplug();
>> /*
>> * The memory might become online by other task, even if you offine it.
>>
>> ...
>>
>
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