linux-kernel - Re: [mm 4.15-rc8] Random oopses under memory pressure.

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Date:   Thu, 18 Jan 2018 18:22:13 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        torvalds@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        akpm@...ux-foundation.org, hannes@...xchg.org,
        iamjoonsoo.kim@....com, mgorman@...hsingularity.net,
        tony.luck@...el.com, vbabka@...e.cz, aarcange@...hat.com,
        hillf.zj@...baba-inc.com, hughd@...gle.com, oleg@...hat.com,
        peterz@...radead.org, riel@...hat.com, srikar@...ux.vnet.ibm.com,
        vdavydov.dev@...il.com, mingo@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Subject: Re: [mm 4.15-rc8] Random oopses under memory pressure.

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