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

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Date:   Thu, 18 Jun 2020 10:03:45 +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.

Thanks,
Daejun