linux-kernel - Re: [PATCH 1/2] mm/hwpoison: fix fail to split THP w/ refcount held

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Date:	Mon, 10 Aug 2015 16:29:18 +0800
From:	Wanpeng Li <wanpeng.li@...mail.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm/hwpoison: fix fail to split THP w/ refcount held

Hi Naoya,

On 8/10/15 4:10 PM, Naoya Horiguchi wrote:
> On Mon, Aug 10, 2015 at 02:32:30PM +0800, Wanpeng Li wrote:
>> THP pages will get a refcount in madvise_hwpoison() w/ MF_COUNT_INCREASED
>> flag, however, the refcount is still held when fail to split THP pages.
>>
>> Fix it by reducing the refcount of THP pages when fail to split THP.
>>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
> It seems that the same conditional put_page() would be added to
> "soft offline: %#lx page already poisoned" branch too, right?

PageHWPoison() is just called before the soft_offline_page() in 
madvise_hwpoion(). I think the PageHWPosion()
check in soft_offline_page() makes more sense for the other 
soft_offline_page() callsites which don't have the
refcount held.

Regards,
Wanpeng Li

>
>> ---
>>   mm/memory-failure.c |    2 ++
>>   1 files changed, 2 insertions(+), 0 deletions(-)
>>
>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>> index 8077b1c..56b8a71 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -1710,6 +1710,8 @@ int soft_offline_page(struct page *page, int flags)
>>   		if (PageAnon(hpage) && unlikely(split_huge_page(hpage))) {
>>   			pr_info("soft offline: %#lx: failed to split THP\n",
>>   				pfn);
>> +			if (flags & MF_COUNT_INCREASED)
>> +				put_page(page);
>>   			return -EBUSY;
>>   		}
>>   	}
>> -- 
>> 1.7.1
>>
>> --
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