linux-kernel - Re: [PATCH v9 3/4] scsi: ufs: L2P map management for HPB read

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Date:   Tue, 01 Sep 2020 09:21:10 +0900
From:   Daejun Park <daejun7.park@...sung.com>
To:     Bart Van Assche <bvanassche@....org>,
        Daejun Park <daejun7.park@...sung.com>,
        "avri.altman@....com" <avri.altman@....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>,
        "tomas.winkler@...el.com" <tomas.winkler@...el.com>,
        ALIM AKHTAR <alim.akhtar@...sung.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: [PATCH v9 3/4] scsi: ufs: L2P map management for HPB read

Hi Bart,
> > +static unsigned int ufshpb_host_map_kbytes = 1024;
> 
> A comment that explains where this value comes from would be welcome.

I will add a follows comment and change defalut value 1024 to 2048. 
"A cache size of 2MB can cache ppn in the 1GB range."

> > +static struct ufshpb_req *ufshpb_get_map_req(struct ufshpb_lu *hpb,
> > +					     struct ufshpb_subregion *srgn)
> > +{
> > +	struct ufshpb_req *map_req;
> > +	struct request *req;
> > +	struct bio *bio;
> > +
> > +	map_req = kmem_cache_alloc(hpb->map_req_cache, GFP_KERNEL);
> > +	if (!map_req)
> > +		return NULL;
> > +
> > +	req = blk_get_request(hpb->sdev_ufs_lu->request_queue,
> > +			      REQ_OP_SCSI_IN, BLK_MQ_REQ_PREEMPT);
> 
> Why BLK_MQ_REQ_PREEMPT? Since this code is only executed while medium access
> commands are processed and since none of these commands have the PREEMPT flag
> set I think that the PREEMPT flag should be left out. Otherwise there probably
> will be weird interactions with runtime suspended devices.

OK, I will remove BLK_MQ_REQ_PREEMPT flag.

> Is it acceptable that the above blk_get_request() call blocks if a UFS device
> has been runtime suspended? If not, consider using the flag BLK_MQ_REQ_NOWAIT
> instead.

The map worker don't issue map requests when the UFS device is in 
runtime suspend. So, I think BLK_MQ_REQ_NOWAIT flags is not needed.

> > +	bio = bio_alloc(GFP_KERNEL, hpb->pages_per_srgn);
> > +	if (!bio) {
> > +		blk_put_request(req);
> > +		goto free_map_req;
> > +	}
> 
> If the blk_get_request() would be modified such that it doesn't wait, this
> call may have to be modified too (GFP_NOWAIT?).
>
> > +	if (rgn->rgn_state == HPB_RGN_INACTIVE) {
> > +		if (atomic_read(&lru_info->active_cnt)
> > +		    == lru_info->max_lru_active_cnt) {
> 
> When splitting a line, please put comparison operators at the end of the line
> instead of at the start, e.g. as follows:
> 
> 		if (atomic_read(&lru_info->active_cnt) ==
> 		    lru_info->max_lru_active_cnt) {

OK, I will change it.
 
> > +	pool_size = DIV_ROUND_UP(ufshpb_host_map_kbytes * 1024, PAGE_SIZE);
> 
> Please use PAGE_ALIGN() to align to the next page boundary.

OK, I will.

Thanks,
Daejun.