Re: [PATCH v2 5/7] mm/hwpoison: don't set migration type twice to avoid hold heavy contend zone->lock

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

On Fri, Aug 23, 2013 at 10:36:38AM -0400, Naoya Horiguchi wrote:
>On Fri, Aug 23, 2013 at 06:30:39PM +0800, Wanpeng Li wrote:
>> v1 -> v2:
>> 	* add more explanation in patch description.
>> 
>> Set pageblock migration type will hold zone->lock which is heavy contended
>> in system to avoid race. However, soft offline page will set pageblock
>> migration type twice during get page if the page is in used, not hugetlbfs
>> page and not on lru list. There is unnecessary to set the pageblock migration
>> type and hold heavy contended zone->lock again if the first round get page
>> have already set the pageblock to right migration type.
>> 
>> The trick here is migration type is MIGRATE_ISOLATE. There are other two parts 
>> can change MIGRATE_ISOLATE except hwpoison. One is memory hoplug, however, we 
>> hold lock_memory_hotplug() which avoid race. The second is CMA which umovable 
>> page allocation requst can't fallback to. So it's safe here.
>> 
>> Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
>> ---
>>  mm/memory-failure.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>> 
>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>> index 297965e..f357c91 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -1426,7 +1426,8 @@ static int __get_any_page(struct page *p, unsigned long pfn, int flags)
>>  	 * was free. This flag should be kept set until the source page
>>  	 * is freed and PG_hwpoison on it is set.
>>  	 */
>> -	set_migratetype_isolate(p, true);
>> +	if (get_pageblock_migratetype(p) == MIGRATE_ISOLATE)
>> +		set_migratetype_isolate(p, true);
>
>Do you really mean "we set MIGRATE_ISOLATE only if it's already set?"
>

Ouch, it's my fault, I will fix it in next version. ;-)

Regards,
Wanpeng Li 

>Thanks,
>Naoya Horiguchi
>
>>  	/*
>>  	 * When the target page is a free hugepage, just remove it
>>  	 * from free hugepage list.
>> -- 
>> 1.8.1.2
>> 
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