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Date:   Thu, 18 Jan 2018 18:22:13 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     Dave Hansen <dave.hansen@linux.intel.com>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        torvalds@linux-foundation.org, kirill.shutemov@linux.intel.com,
        akpm@linux-foundation.org, hannes@cmpxchg.org,
        iamjoonsoo.kim@lge.com, mgorman@techsingularity.net,
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        vdavydov.dev@gmail.com, mingo@kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org
Subject: Re: [mm 4.15-rc8] Random oopses under memory pressure.
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On Thu 18-01-18 18:40:26, Kirill A. Shutemov wrote:
[...]
> +	/*
> +	 * Make sure that pages are in the same section before doing pointer
> +	 * arithmetics.
> +	 */
> +	if (page_to_section(pvmw->page) != page_to_section(page))
> +		return false;

OK, THPs shouldn't cross memory sections AFAIK. My brain is meltdown
these days so this might be a completely stupid question. But why don't
you simply compare pfns? This would be just simpler, no?

> +
> +	if (page < pvmw->page)
> +		return false;
> +
> +	/* THP can be referenced by any subpage */
> +	if (page - pvmw->page >= hpage_nr_pages(pvmw->page))
> +		return false;
> +
>  	return true;
>  }
>  
> -- 
>  Kirill A. Shutemov

-- 
Michal Hocko
SUSE Labs