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Date: Fri, 18 Mar 2016 00:52:54 +0900
Message-ID: <CAAmzW4MNdFHSSTpCfWqy7oDtkR_Hfu2dZa_LW97W8J5vr5m4tg@mail.gmail.com>
Subject: Re: Suspicious error for CMA stress test
From: Joonsoo Kim <js1304@gmail.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Hanjun Guo <guohanjun@huawei.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>,
        Laura Abbott <labbott@redhat.com>,
        "linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Sasha Levin <sasha.levin@oracle.com>,
        Laura Abbott <lauraa@codeaurora.org>, qiuxishi <qiuxishi@huawei.com>,
        Catalin Marinas <Catalin.Marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>, Arnd Bergmann <arnd@arndb.de>,
        dingtinahong <dingtianhong@huawei.com>, chenjie6@huawei.com,
        "linux-mm@kvack.org" <linux-mm@kvack.org>
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2016-03-18 0:43 GMT+09:00 Vlastimil Babka <vbabka@suse.cz>:
> On 03/17/2016 10:24 AM, Hanjun Guo wrote:
>>
>> On 2016/3/17 14:54, Joonsoo Kim wrote:
>>>
>>> On Wed, Mar 16, 2016 at 05:44:28PM +0800, Hanjun Guo wrote:
>>>>
>>>> On 2016/3/14 15:18, Joonsoo Kim wrote:
>>>>>
>>>>> On Mon, Mar 14, 2016 at 08:06:16AM +0100, Vlastimil Babka wrote:
>>>>>>
>>>>>> On 03/14/2016 07:49 AM, Joonsoo Kim wrote:
>>>>>>>
>>>>>>> On Fri, Mar 11, 2016 at 06:07:40PM +0100, Vlastimil Babka wrote:
>>>>>>>>
>>>>>>>> On 03/11/2016 04:00 PM, Joonsoo Kim wrote:
>>>>>>>>
>>>>>>>> How about something like this? Just and idea, probably buggy
>>>>>>>> (off-by-one etc.).
>>>>>>>> Should keep away cost from <pageblock_order iterations at the
>>>>>>>> expense of the
>>>>>>>> relatively fewer >pageblock_order iterations.
>>>>>>>
>>>>>>> Hmm... I tested this and found that it's code size is a little bit
>>>>>>> larger than mine. I'm not sure why this happens exactly but I guess
>>>>>>> it would be
>>>>>>> related to compiler optimization. In this case, I'm in favor of my
>>>>>>> implementation because it looks like well abstraction. It adds one
>>>>>>> unlikely branch to the merge loop but compiler would optimize it to
>>>>>>> check it once.
>>>>>>
>>>>>> I would be surprised if compiler optimized that to check it once, as
>>>>>> order increases with each loop iteration. But maybe it's smart
>>>>>> enough to do something like I did by hand? Guess I'll check the
>>>>>> disassembly.
>>>>>
>>>>> Okay. I used following slightly optimized version and I need to
>>>>> add 'max_order = min_t(unsigned int, MAX_ORDER, pageblock_order + 1)'
>>>>> to yours. Please consider it, too.
>>>>
>>>> Hmm, this one is not work, I still can see the bug is there after
>>>> applying
>>>> this patch, did I miss something?
>>>
>>> I may find that there is a bug which was introduced by me some time
>>> ago. Could you test following change in __free_one_page() on top of
>>> Vlastimil's patch?
>>>
>>> -page_idx = pfn & ((1 << max_order) - 1);
>>> +page_idx = pfn & ((1 << MAX_ORDER) - 1);
>>
>>
>> I tested Vlastimil's patch + your change with stress for more than half
>> hour, the bug
>> I reported is gone :)
>
>
> Oh, ok, will try to send proper patch, once I figure out what to write in
> the changelog :)

Thanks in advance!

Thanks.