Re: [PATCH v2] mm/ksm: ignore STABLE_FLAG of rmap_item->address in rmap_walk_ksm

From: Jia He <hejianet@gmail.com>
To: Suzuki K Poulose <Suzuki.Poulose@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
	Minchan Kim <minchan@kernel.org>,
	Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>,
	Arvind Yadav <arvind.yadav.cs@gmail.com>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	jia.he@hxt-semitech.com, Hugh Dickins <hughd@google.com>
Subject: Re: [PATCH v2] mm/ksm: ignore STABLE_FLAG of rmap_item->address in rmap_walk_ksm
Date: Thu, 24 May 2018 17:36:57 +0800	[thread overview]
Message-ID: <2c220e3d-8ff1-f9a9-9038-fff38952b8b1@gmail.com> (raw)
In-Reply-To: <575857e6-c8ec-efa0-6434-b78a513aeaba@arm.com>


On 5/24/2018 5:01 PM, Suzuki K Poulose Wrote:
> On 24/05/18 09:50, Jia He wrote:
>> Hi Suzuki
>>
>> On 5/24/2018 4:44 PM, Suzuki K Poulose Wrote:
>>> On 14/05/18 10:45, Suzuki K Poulose wrote:
>>>> On 10/05/18 00:31, Andrew Morton wrote:
>>>>> On Fri,  4 May 2018 11:11:46 +0800 Jia He <hejianet@gmail.com> wrote:
>>>>>
>>>>>> In our armv8a server(QDF2400), I noticed lots of WARN_ON caused by PAGE_SIZE
>>>>>> unaligned for rmap_item->address under memory pressure tests(start 20 guests
>>>>>> and run memhog in the host).
>>>>>>
>>>>>> ...
>>>>>>
>>>>>> In rmap_walk_ksm, the rmap_item->address might still have the STABLE_FLAG,
>>>>>> then the start and end in handle_hva_to_gpa might not be PAGE_SIZE aligned.
>>>>>> Thus it will cause exceptions in handle_hva_to_gpa on arm64.
>>>>>>
>>>>>> This patch fixes it by ignoring(not removing) the low bits of address when
>>>>>> doing rmap_walk_ksm.
>>>>>>
>>>>>> Signed-off-by: jia.he@hxt-semitech.com
>>>>>
>>>>> I assumed you wanted this patch to be committed as
>>>>> From:jia.he@hxt-semitech.com rather than From:hejianet@gmail.com, so I
>>>>> made that change.  Please let me know if this was inappropriate.
>>>>>
>>>>> You can do this yourself by adding an explicit From: line to the very
>>>>> start of the patch's email text.
>>>>>
>>>>> Also, a storm of WARN_ONs is pretty poor behaviour.  Is that the only
>>>>> misbehaviour which this bug causes?  Do you think the fix should be
>>>>> backported into earlier kernels?
>>>>>
>>>
>>>
>>> Jia, Andrew,
>>>
>>> What is the status of this patch ?
>>>
>>> Suzuki
>> I thought the patch is merged into mmotm tree.
>> http://www.ozlabs.org/~akpm/mmotm/series
>> But I don't know what is the next step.
> 
> Hi Jia,
> 
> Thanks for the update. I think that should eventually hit mainline. When it does,
> please could you send the patch to stable kernel versions too ?
> 
> Usually having a "Cc: stable@kernel.vger.org" in the original patch (for
> critical fixes) would have done the trick. But since we don't have it,
> please send it following the stable kernel rules.
> 
> Cheers
> Suzuki
> 
Ok,thanks for pointing
-- 
Cheers,
Jia