linux-kernel - Re: [PATCH 3/3] Fix unsuitable behavior for poisoned tail pages of THP.

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Date:	Tue, 25 Jan 2011 23:46:35 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Jin Dongming <jin.dongming@...css.fujitsu.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	AKPM　 <akpm@...ux-foundation.org>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Huang Ying <ying.huang@...el.com>,
	LKLM <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] Fix unsuitable behavior for poisoned tail pages of
 THP.

On Tue, Jan 25, 2011 at 02:46:32PM +0900, Jin Dongming wrote:
> When a tail page of THP is poisoned, memory-failure will do
> nothing except setting poison flag, while the expected behavior is
> that the process, who is using the poisoned tail page, should be
> killed.
> 
> The above problem is caused by lru checking of the poisoned tail page
> of THP. Because PG_lru flag is only set on the head page of
> THP, the check always consider the poisoned tail page as NON
> lru page.
> 
> So avoid checking NON lru for THP, as like as hugetlb.
> 
> Signed-off-by: Jin Dongming <jin.dongming@...css.fujitsu.com>
> Reviewed-by: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
> ---
>  mm/memory-failure.c |   27 +++++++++++++++------------
>  1 files changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 5396603..44a1bdf 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1046,19 +1046,22 @@ int __memory_failure(unsigned long pfn, int trapno, int flags)
>  	 * The check (unnecessarily) ignores LRU pages being isolated and
>  	 * walked by the page reclaim code, however that's not a big loss.
>  	 */
> -	if (!PageLRU(p) && !PageHuge(p))
> -		shake_page(p, 0);
> -	if (!PageLRU(p) && !PageHuge(p)) {
> -		/*
> -		 * shake_page could have turned it free.
> -		 */
> -		if (is_free_buddy_page(p)) {
> -			action_result(pfn, "free buddy, 2nd try", DELAYED);
> -			return 0;
> +	if (!PageCompound(p)) {

Here the check could become a:

        if (!PageHuge(p) && !PageTransCompound(p))

so the whole branch is optimized away at build time when both
hugetlbfs and THP are set =n (or in archs not supporting either of
those).

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