linux-kernel - Re: [PATCH v6 04/10] scsi: ufshpb: Make eviction depends on region's reads

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Date:   Thu, 25 Mar 2021 13:34:21 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Avri Altman <avri.altman@....com>
Cc:     "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org, Bart Van Assche <bvanassche@....org>,
        yongmyung lee <ymhungry.lee@...sung.com>,
        Daejun Park <daejun7.park@...sung.com>,
        alim.akhtar@...sung.com, asutoshd@...eaurora.org,
        Zang Leigang <zangleigang@...ilicon.com>,
        Avi Shchislowski <avi.shchislowski@....com>,
        Bean Huo <beanhuo@...ron.com>, stanley.chu@...iatek.com
Subject: Re: [PATCH v6 04/10] scsi: ufshpb: Make eviction depends on region's
 reads

On 2021-03-22 16:10, Avri Altman wrote:
> In host mode, eviction is considered an extreme measure.
> verify that the entering region has enough reads, and the exiting
> region has much less reads.
> 
> Signed-off-by: Avri Altman <avri.altman@....com>
> ---
>  drivers/scsi/ufs/ufshpb.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/ufs/ufshpb.c b/drivers/scsi/ufs/ufshpb.c
> index a1519cbb4ce0..5e757220d66a 100644
> --- a/drivers/scsi/ufs/ufshpb.c
> +++ b/drivers/scsi/ufs/ufshpb.c
> @@ -17,6 +17,7 @@
>  #include "../sd.h"
> 
>  #define ACTIVATION_THRESHOLD 8 /* 8 IOs */
> +#define EVICTION_THRESHOLD (ACTIVATION_THRESHOLD << 5) /* 256 IOs */
> 
>  /* memory management */
>  static struct kmem_cache *ufshpb_mctx_cache;
> @@ -1047,6 +1048,13 @@ static struct ufshpb_region
> *ufshpb_victim_lru_info(struct ufshpb_lu *hpb)
>  		if (ufshpb_check_srgns_issue_state(hpb, rgn))
>  			continue;
> 
> +		/*
> +		 * in host control mode, verify that the exiting region
> +		 * has less reads
> +		 */
> +		if (hpb->is_hcm && rgn->reads > (EVICTION_THRESHOLD >> 1))
> +			continue;
> +
>  		victim_rgn = rgn;
>  		break;
>  	}
> @@ -1219,7 +1227,7 @@ static int ufshpb_issue_map_req(struct ufshpb_lu 
> *hpb,
> 
>  static int ufshpb_add_region(struct ufshpb_lu *hpb, struct 
> ufshpb_region *rgn)
>  {
> -	struct ufshpb_region *victim_rgn;
> +	struct ufshpb_region *victim_rgn = NULL;
>  	struct victim_select_info *lru_info = &hpb->lru_info;
>  	unsigned long flags;
>  	int ret = 0;
> @@ -1246,7 +1254,15 @@ static int ufshpb_add_region(struct ufshpb_lu
> *hpb, struct ufshpb_region *rgn)
>  			 * It is okay to evict the least recently used region,
>  			 * because the device could detect this region
>  			 * by not issuing HPB_READ
> +			 *
> +			 * in host control mode, verify that the entering
> +			 * region has enough reads
>  			 */
> +			if (hpb->is_hcm && rgn->reads < EVICTION_THRESHOLD) {
> +				ret = -EACCES;
> +				goto out;
> +			}
> +

I cannot understand the logic behind this. A rgn which host chooses to 
activate,
is in INACTIVE state now, if its rgn->reads < 256, then don't activate 
it.
Could you please elaborate?

Thanks,
Can Guo.

>  			victim_rgn = ufshpb_victim_lru_info(hpb);
>  			if (!victim_rgn) {
>  				dev_warn(&hpb->sdev_ufs_lu->sdev_dev,