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Subject: Re: Another approach of UFSHPB
To:     Avri Altman <Avri.Altman@wdc.com>,
        "daejun7.park@samsung.com" <daejun7.park@samsung.com>,
        yongmyung lee <ymhungry.lee@samsung.com>,
        "James E . J . Bottomley" <jejb@linux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc:     ALIM AKHTAR <alim.akhtar@samsung.com>,
        "asutoshd@codeaurora.org" <asutoshd@codeaurora.org>,
        Zang Leigang <zangleigang@hisilicon.com>,
        Avi Shchislowski <Avi.Shchislowski@wdc.com>,
        Bean Huo <beanhuo@micron.com>,
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        "stanley.chu@mediatek.com" <stanley.chu@mediatek.com>,
        MOHAMMED RAFIQ KAMAL BASHA <md.rafiq@samsung.com>,
        Sang-yoon Oh <sangyoon.oh@samsung.com>,
        Jinyoung CHOI <j-young.choi@samsung.com>,
        Adel Choi <adel.choi@samsung.com>,
        BoRam Shin <boram.shin@samsung.com>,
        Sung-Jun Park <sungjun07.park@samsung.com>
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From:   Bart Van Assche <bvanassche@acm.org>
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Date:   Tue, 26 May 2020 10:03:59 -0700
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On 2020-05-25 23:15, Avri Altman wrote:
>> On 2020-05-24 22:40, Daejun Park wrote:
>>> The HPB driver is close to the UFS core function, but it is not essential
>>> for operating UFS device. With reference to this article
>>> (https://lwn.net/Articles/645810/), we implemented extended UFS-feature
>>> as bus model. Because the HPB driver consumes the user's main memory, it
>> should
>>> support bind / unbind functionality as needed. We implemented the HPB
>> driver
>>> can be unbind / unload on runtime.
>>
>> I do not agree that the bus model is the best choice for freeing cache
>> memory if it is no longer needed. A shrinker is probably a much better
>> choice because the callback functions in a shrinker get invoked when a
>> system is under memory pressure. See also register_shrinker(),
>> unregister_shrinker() and struct shrinker in include/linux/shrinker.h.
>
> Since this discussion is closely related to cache allocation,
> What is your opinion about allocating the pages dynamically as the regions
> Are being activated/deactivated, in oppose of how it is done today - 
> Statically on init for the entire max-active-subregions?

Memory that is statically allocated cannot be used for any other purpose
(e.g. page cache) without triggering the associated shrinker. As far as
I know shrinkers are only triggered when (close to) out of memory. So
dynamically allocating memory as needed is probably a better strategy
than statically allocating the entire region at initialization time.

Thanks,

Bart.