linux-kernel - Re: [PATCH] lightnvm: pblk: fix changing GC group list for a line

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Date:   Mon, 2 Oct 2017 14:43:44 +0300
From:   Rakesh Pandit <rakesh@...era.com>
To:     Javier González <jg@...htnvm.io>
CC:     Matias Bjørling <mb@...htnvm.io>,
        <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lightnvm: pblk: fix changing GC group list for a line

On Mon, Oct 02, 2017 at 01:27:42PM +0200, Javier González wrote:
> > On 28 Sep 2017, at 16.40, Rakesh Pandit <rakesh@...era.com> wrote:
> > 
> > pblk_line_gc_list seems to had a bug since the introduction of pblk in
> > getting GC list for a line.  In b20ba1bc7 while redesigning GC
> > algorithm it was not fixed correctly.  The problem is that even if
> > valid sector count (vsc) is less that mid_thrs (threshold for GC mid
> > list) it would always satisfy 'vsc < high_thrs' as high_thrs >
> > mid_thrs always.
> > 
> > Fixes: a4bd217b4("lightnvm: physical block device (pblk) target")
> > Signed-off-by: Rakesh Pandit <rakesh@...era.com>
> > ---
> > drivers/lightnvm/pblk-core.c | 10 +++++-----
> > 1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/lightnvm/pblk-core.c b/drivers/lightnvm/pblk-core.c
> > index 8150164..93a58ed 100644
> > --- a/drivers/lightnvm/pblk-core.c
> > +++ b/drivers/lightnvm/pblk-core.c
> > @@ -295,16 +295,16 @@ struct list_head *pblk_line_gc_list(struct pblk *pblk, struct pblk_line *line)
> > 			line->gc_group = PBLK_LINEGC_FULL;
> > 			move_list = &l_mg->gc_full_list;
> > 		}
> > -	} else if (vsc < lm->high_thrs) {
> > -		if (line->gc_group != PBLK_LINEGC_HIGH) {
> > -			line->gc_group = PBLK_LINEGC_HIGH;
> > -			move_list = &l_mg->gc_high_list;
> > -		}
> > 	} else if (vsc < lm->mid_thrs) {
> > 		if (line->gc_group != PBLK_LINEGC_MID) {
> > 			line->gc_group = PBLK_LINEGC_MID;
> > 			move_list = &l_mg->gc_mid_list;
> > 		}
> > +	} else if (vsc < lm->high_thrs) {
> > +		if (line->gc_group != PBLK_LINEGC_HIGH) {
> > +			line->gc_group = PBLK_LINEGC_HIGH;
> > +			move_list = &l_mg->gc_high_list;
> > +		}
> > 	} else if (vsc < line->sec_in_line) {
> > 		if (line->gc_group != PBLK_LINEGC_LOW) {
> > 			line->gc_group = PBLK_LINEGC_LOW;
> > --
> > 2.9.3
> 
> You're right that the naming for high/mid/low was not updated when
> aligning vsc with GC thresholds. But the fix should be making high,
> being high, instead of reordering when moving into the GC bucket.
> 
> Does it make sense to you?

Yes.

> 
> diff --git i/drivers/lightnvm/pblk-init.c w/drivers/lightnvm/pblk-init.c
> index 7cf4b536d899..bc5c6cc12ad5 100644
> --- i/drivers/lightnvm/pblk-init.c
> +++ w/drivers/lightnvm/pblk-init.c
> @@ -675,8 +675,8 @@ static int pblk_lines_init(struct pblk *pblk)
>         lm->blk_bitmap_len = BITS_TO_LONGS(geo->nr_luns) * sizeof(long);
>         lm->sec_bitmap_len = BITS_TO_LONGS(lm->sec_per_line) * sizeof(long);
>         lm->lun_bitmap_len = BITS_TO_LONGS(geo->nr_luns) * sizeof(long);
> -       lm->high_thrs = lm->sec_per_line / 2;
> -       lm->mid_thrs = lm->sec_per_line / 4;
> +       lm->high_thrs = lm->sec_per_line / 4;
> +       lm->mid_thrs = lm->sec_per_line / 2;
>         lm->meta_distance = (geo->nr_luns / 2) * pblk->min_write_pgs;
> 
>         /* Calculate necessary pages for smeta. See comment over struct

Regards,