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

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Message-ID: <20180119100259.rwq3evikkemtv7q5@node.shutemov.name>
Date:   Fri, 19 Jan 2018 13:02:59 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Michal Hocko <mhocko@...nel.org>
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, Jan 18, 2018 at 06:22:13PM +0100, Michal Hocko wrote:
> 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?

In original code, we already had pvmw->page around and I thought it would
be easier to get page for the pte intead of looking for pfn for both
sides.

We these changes it's no longer the case.

Do you care enough to send a patch? :)

-- 
 Kirill A. Shutemov