linux-kernel - RE: [RFC PATCH v2 4/5] scsi: ufs: L2P map management for HPB read

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Date:   Fri, 19 Jun 2020 09:16:40 +0900
From:   Daejun Park <daejun7.park@...sung.com>
To:     Avri Altman <Avri.Altman@....com>,
        Daejun Park <daejun7.park@...sung.com>,
        ALIM AKHTAR <alim.akhtar@...sung.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        "beanhuo@...ron.com" <beanhuo@...ron.com>,
        "stanley.chu@...iatek.com" <stanley.chu@...iatek.com>,
        "cang@...eaurora.org" <cang@...eaurora.org>,
        "bvanassche@....org" <bvanassche@....org>,
        "tomas.winkler@...el.com" <tomas.winkler@...el.com>
CC:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sang-yoon Oh <sangyoon.oh@...sung.com>,
        Sung-Jun Park <sungjun07.park@...sung.com>,
        yongmyung lee <ymhungry.lee@...sung.com>,
        Jinyoung CHOI <j-young.choi@...sung.com>,
        Adel Choi <adel.choi@...sung.com>,
        BoRam Shin <boram.shin@...sung.com>
Subject: RE: [RFC PATCH v2 4/5] scsi: ufs: L2P map management for HPB read

> > > +
> > > > +static struct ufshpb_map_ctx *ufshpb_get_map_ctx(struct ufshpb_lu
> > *hpb)
> > > > +{
> > > > +       struct ufshpb_map_ctx *mctx;
> > > > +       int i, j;
> > > > +
> > > > +       mctx = mempool_alloc(ufshpb_drv.ufshpb_mctx_pool, GFP_KERNEL);
> > > > +       if (!mctx)
> > > > +               return NULL;
> > > So you use ufshpb_host_map_kbytes as the min_nr in your
> > mempool_create,
> > > But you know that you need max_lru_active_cnt x srgns_per_rgn such
> > mapping context elements.
> > > So you are
> > > a) failing to provide the slab allocator an information that you already have,
> > and
> > > b) selecting from a finite pool will assure that you'll never exceed max-
> > active-regions,
> > >    even if some corner case fails your logic.
> > It was intend to provide user-configurable pre-allocated memory to reduce
> > latency due to memory allocation. The value of ufshpb_host_map_kbytes can
> > be set to max_lru_active_cnt x srgns_per_rgn, if the user want to.
> Ok, I see your point.
> It is as if you expect that a "user" will query the unit descriptors first,
> Make some calculations, and then will run modprobe with the proper value.
> Are you assuming that an "intelligent" user does all that?
> 
> The reasonable scenario IMO, is that OEMs will initiate a service in their
> ramdisk/init.rc with some default value.
> 
> Don't you see the damage potential in using a wrong value here?
> 
I understand your scenario. I will remove module parameter and set min_nr
value of memory pool as "max_lru_active_cnt x srgns_per_rgn" size.

Thanks,
Daejun