linux-kernel - Re: Another approach of UFSHPB

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Date:   Mon, 25 May 2020 07:56:54 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     daejun7.park@...sung.com, yongmyung lee <ymhungry.lee@...sung.com>,
        Avri Altman <Avri.Altman@....com>,
        "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     ALIM AKHTAR <alim.akhtar@...sung.com>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        Zang Leigang <zangleigang@...ilicon.com>,
        Avi Shchislowski <Avi.Shchislowski@....com>,
        Bean Huo <beanhuo@...ron.com>,
        "cang@...eaurora.org" <cang@...eaurora.org>,
        "stanley.chu@...iatek.com" <stanley.chu@...iatek.com>,
        MOHAMMED RAFIQ KAMAL BASHA <md.rafiq@...sung.com>,
        Sang-yoon Oh <sangyoon.oh@...sung.com>,
        Jinyoung CHOI <j-young.choi@...sung.com>,
        Adel Choi <adel.choi@...sung.com>,
        BoRam Shin <boram.shin@...sung.com>,
        Sung-Jun Park <sungjun07.park@...sung.com>
Subject: Re: Another approach of UFSHPB

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.

>> Should these parameters be per module or per UFS device?
> 
> I think it is necessary to take parameters for each module. 
> This is because each extended UFS-feature module has different functions
> and may require different parameters.

My question was a rhetorical question. Please choose per device
parameters when appropriate instead of module parameters.

Thanks,

Bart.