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SubjectRe: [PATCH v5 03/14] memory-hotplug: remove redundant codes
Hi Kamezawa-san,

Thanks for the reviewing. Please see below. :)

On 12/26/2012 11:20 AM, Kamezawa Hiroyuki wrote:
> (2012/12/24 21:09), Tang Chen wrote:
>> From: Wen Congyang<wency@cn.fujitsu.com>
>>
>> offlining memory blocks and checking whether memory blocks are offlined
>> are very similar. This patch introduces a new function to remove
>> redundant codes.
>>
>> Signed-off-by: Wen Congyang<wency@cn.fujitsu.com>
>> ---
>> mm/memory_hotplug.c | 101 ++++++++++++++++++++++++++++-----------------------
>> 1 files changed, 55 insertions(+), 46 deletions(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index d43d97b..dbb04d8 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1381,20 +1381,14 @@ int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
>> return __offline_pages(start_pfn, start_pfn + nr_pages, 120 * HZ);
>> }
>>
>> -int remove_memory(u64 start, u64 size)
>
> please add explanation of this function here. If (*func) returns val other than 0,
> this function will fail and returns callback's return value...right ?
>

Yes, it will always return the func()'s return value. I'll add the
comment here. :)

>
>> +static int walk_memory_range(unsigned long start_pfn, unsigned long end_pfn,
>> + void *arg, int (*func)(struct memory_block *, void *))
>> {
>> struct memory_block *mem = NULL;
>> struct mem_section *section;
>> - 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:
>
> Shouldn't we check lock is held here ? (VM_BUG_ON(!mutex_is_locked(&mem_hotplug_mutex);

Well, I think, after applying this patch, walk_memory_range() will be
a separated function. And it can be used somewhere else where we don't
hold this lock. But for now, we can do this check. :)

>
>
>> for (pfn = start_pfn; pfn< end_pfn; pfn += PAGES_PER_SECTION) {
>> section_nr = pfn_to_section_nr(pfn);
>> if (!present_section_nr(section_nr))
>> @@ -1411,22 +1405,61 @@ repeat:
>> if (!mem)
>> continue;
>>
>> - ret = offline_memory_block(mem);
>> + ret = func(mem, arg);
>> if (ret) {
>> - if (return_on_error) {
>> - kobject_put(&mem->dev.kobj);
>> - return ret;
>> - } else {
>> - retry = 1;
>> - }
>> + kobject_put(&mem->dev.kobj);
>> + return ret;
>> }
>> }
>>
>> if (mem)
>> kobject_put(&mem->dev.kobj);
>>
>> - if (retry) {
>> - return_on_error = 1;
>> + return 0;
>> +}
>> +
>> +static int offline_memory_block_cb(struct memory_block *mem, void *arg)
>> +{
>> + int *ret = arg;
>> + int error = offline_memory_block(mem);
>> +
>> + if (error != 0&& *ret == 0)
>> + *ret = error;
>> +
>> + return 0;
>
> Always returns 0 and run through all mem blocks for scan-and-retry, right ?
> You need explanation here !

Yes, I'll add the comment. :)

>
>
>> +}
>> +
>> +static int is_memblock_offlined_cb(struct memory_block *mem, void *arg)
>> +{
>> + int ret = !is_memblock_offlined(mem);
>> +
>> + if (unlikely(ret))
>> + pr_warn("removing memory fails, because memory "
>> + "[%#010llx-%#010llx] is onlined\n",
>> + PFN_PHYS(section_nr_to_pfn(mem->start_section_nr)),
>> + PFN_PHYS(section_nr_to_pfn(mem->end_section_nr + 1))-1);
>> +
>> + return ret;
>> +}
>> +
>> +int remove_memory(u64 start, u64 size)
>> +{
>> + unsigned long start_pfn, end_pfn;
>> + int ret = 0;
>> + int retry = 1;
>> +
>> + start_pfn = PFN_DOWN(start);
>> + end_pfn = start_pfn + PFN_DOWN(size);
>> +
>> +repeat:
>
> please explan why you repeat here .

This repeat is add in patch1. It aims to solve the problem we were
talking about in patch1. I'll add the comment here. :)

>
>> + walk_memory_range(start_pfn, end_pfn,&ret,
>> + offline_memory_block_cb);
>> + if (ret) {
>> + if (!retry)
>> + return ret;
>> +
>> + retry = 0;
>> + ret = 0;
>> goto repeat;
>> }
>>
>> @@ -1444,37 +1477,13 @@ repeat:
>> * memory blocks are offlined.
>> */
>>
>> - 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;
>> -
>> - ret = is_memblock_offlined(mem);
>> - if (!ret) {
>> - pr_warn("removing memory fails, because memory "
>> - "[%#010llx-%#010llx] is onlined\n",
>> - PFN_PHYS(section_nr_to_pfn(mem->start_section_nr)),
>> - PFN_PHYS(section_nr_to_pfn(mem->end_section_nr + 1)) - 1);
>> -
>> - kobject_put(&mem->dev.kobj);
>> - unlock_memory_hotplug();
>> - return ret;
>> - }
>
> please explain what you do here. confirming all memory blocks are offlined
> before returning 0 ....right ?

Will be added. :)

Thanks. :)

>
>> + ret = walk_memory_range(start_pfn, end_pfn, NULL,
>> + is_memblock_offlined_cb);
>> + if (ret) {
>> + unlock_memory_hotplug();
>> + return ret;
>> }
>>
>> - if (mem)
>> - kobject_put(&mem->dev.kobj);
>> unlock_memory_hotplug();
>>
>> return 0;
>>
>
> Thanks,
> -Kame
>
>



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