linux-kernel - Re: [PATCH V3] powerpc/mm: Fix Multi hit ERAT cause by recent THP update

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Message-ID: <1455512997.16012.24.camel@gmail.com>
Date:	Mon, 15 Feb 2016 16:09:57 +1100
From:	Balbir Singh <bsingharora@...il.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
	akpm@...ux-foundation.org,
	Mel Gorman <mgorman@...hsingularity.net>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3] powerpc/mm: Fix Multi hit ERAT cause by recent THP
 update


> Now we can't depend for mm_cpumask, a parallel find_linux_pte_hugepte
> can happen outside that. Now i had a variant for kick_all_cpus_sync that
> ignored idle cpus. But then that needs more verification.
> 
> http://article.gmane.org/gmane.linux.ports.ppc.embedded/81105
Can be racy as a CPU moves from non-idle to idle

In

> +     pmd_hugepage_update(vma->vm_mm, address, pmdp, ~0UL, 0);
> +     /*
> +      * This ensures that generic code that rely on IRQ disabling
> +      * to prevent a parallel THP split work as expected.
> +      */
> +     kick_all_cpus_sync();

pmdp_invalidate()->pmd_hugepage_update() can still run in parallel with 
find_linux_pte_or_hugepte() and race.. Am I missing something?

Balbir Singh