From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
To: Balbir Singh <bsingharora@gmail.com>,
benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au,
akpm@linux-foundation.org,
Mel Gorman <mgorman@techsingularity.net>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH V3] powerpc/mm: Fix Multi hit ERAT cause by recent THP update
Date: Mon, 15 Feb 2016 16:31:59 +0530 [thread overview]
Message-ID: <87d1ryfd94.fsf@linux.vnet.ibm.com> (raw)
In-Reply-To: <1455512997.16012.24.camel@gmail.com>
Balbir Singh <bsingharora@gmail.com> writes:
>> 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?
>
Yes. But then we make sure that the pte_t returned by
find_linux_pte_or_hugepte doesn't change to a regular pmd entry by using
that kick. Now callers of find_lnux_pte_or_hugepte will check for
_PAGE_PRESENT. So if it called before
pmd_hugepage_update(_PAGE_PRESENT), we wait for the caller to finish the
usage (via kick()). Or they bail out after finding _PAGE_PRESENT cleared.
-aneesh
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next prev parent reply other threads:[~2016-02-15 11:02 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-09 1:20 [PATCH V3] powerpc/mm: Fix Multi hit ERAT cause by recent THP update Aneesh Kumar K.V
2016-02-09 12:16 ` [V3] " Michael Ellerman
2016-02-14 5:32 ` Aneesh Kumar K.V
2016-02-15 2:44 ` [PATCH V3] " Balbir Singh
2016-02-15 4:37 ` Aneesh Kumar K.V
2016-02-15 5:09 ` Balbir Singh
2016-02-15 11:01 ` Aneesh Kumar K.V [this message]
2016-02-16 5:20 ` Balbir Singh
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