[PATCH v2] erofs: add a global page pool for lz4 decompression

[Chunhai Guo]

On 2024/1/10 14:45, Chunhai Guo wrote:
> On 2024/1/9 21:08, Gao Xiang wrote:
>> [你通常不会收到来自 hsiangkao at linux.alibaba.com 的电子邮件。请访问 
>> https://aka.ms/LearnAboutSenderIdentification，以了解这一点为什么很重要]
>>
>> Hi Chunhai,
>>
>> On 2024/1/9 15:41, Chunhai Guo wrote:
>>> Using a global page pool for LZ4 decompression significantly reduces 
>>> the
>>> time spent on page allocation in low memory scenarios.
>>>
>>> The table below shows the reduction in time spent on page allocation 
>>> for
>>> LZ4 decompression when using a global page pool.  The results were
>>> obtained from multi-app launch benchmarks on ARM64 Android devices
>>> running the 5.15 kernel with an 8-core CPU and 8GB of memory. In the
>>> benchmark, we launched 16 frequently-used apps, and the camera app was
>>> the last one in each round. The data in the table is the average 
>>> time of
>>> camera app for each round.
>>> After using the page pool, there was an average improvement of 150ms in
>>> the launch time of the camera app, which was obtained from systrace 
>>> log.
>>> +--------------+---------------+--------------+---------+
>>> |              | w/o page pool | w/ page pool |  diff   |
>>> +--------------+---------------+--------------+---------+
>>> | Average (ms) |     3434      |      21      | -99.38% |
>>> +--------------+---------------+--------------+---------+
>>>
>>> Based on the benchmark logs, 64 pages are sufficient for 95% of
>>> scenarios. This value can be adjusted from the module parameter. The
>>> default value is 0.
>>>
>>> This patch currently only supports the LZ4 decompressor, other
>>> decompressors will be supported in the next step.
>>>
>>> Signed-off-by: Chunhai Guo <guochunhai at vivo.com>
>>
>> This patch looks good to me, yet we're in the merge window for v6.8.
>> I will address it after -rc1 is out since no stable tag these days.
>>
>> Also it would be better to add some results of changing max_distance
>> if you have more time to test.
>
> OK. I will reply to this email when the experiment is finished.

Dear Xiang,

The experiment is done and table below shows the results. We can find 
that a 16k sliding window reduces 38.2% of time used in page allocation 
for LZ4 decompression compared to a 64k sliding window. However, using a 
global page pool is still far better than both of them.

+--------------+---------------+--------------+---------+
|              |   64k window  |  16k window  |  diff   |
+--------------+---------------+--------------+---------+
| Average (ms) |     3364      |      2079    | -38.2%  |
+--------------+---------------+--------------+---------+

Thanks,

>
> Thanks.
>
>>
>> Thanks,
>> Gao Xiang
>
>