linux-kernel - Re: [PATCH 11/63] mm: Close races between THP migration and PMD numa clearing

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Message-ID: <20130930151802.GG2425@suse.de>
Date:	Mon, 30 Sep 2013 16:18:02 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Rik van Riel <riel@...hat.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, jstancek@...hat.com
Subject: Re: [PATCH 11/63] mm: Close races between THP migration and PMD numa
 clearing

On Mon, Sep 30, 2013 at 10:10:48AM -0400, Rik van Riel wrote:
> On Mon, 30 Sep 2013 09:52:59 +0100
> Mel Gorman <mgorman@...e.de> wrote:
> 
> > On Fri, Sep 27, 2013 at 02:26:56PM +0100, Mel Gorman wrote:
> > > @@ -1732,9 +1732,9 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
> > >  	entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
> > >  	entry = pmd_mkhuge(entry);
> > >  
> > > -	page_add_new_anon_rmap(new_page, vma, haddr);
> > > -
> > > +	pmdp_clear_flush(vma, address, pmd);
> > >  	set_pmd_at(mm, haddr, pmd, entry);
> > > +	page_add_new_anon_rmap(new_page, vma, haddr);
> > >  	update_mmu_cache_pmd(vma, address, &entry);
> > >  	page_remove_rmap(page);
> > >  	/*
> > 
> > pmdp_clear_flush should have used haddr
> 
> Dang, we both discovered this over the weekend? :)
> 

Saw it this morning running a debugging build.

> In related news, it looks like update_mmu_cache_pmd should
> probably use haddr, too...
> 

Does anything care? Other calls to update_mmu_cache_pmd are using address
and not haddr so if this is a problem, it's a problem in a few places. Of
the arches that support THP, only sparc appears to do anything useful and
it shifts the address HPAGE_SHIFT so it does not matter if the address
was aligned or not.

-- 
Mel Gorman
SUSE Labs
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