linux-kernel - Re: [PATCH] zram: do not set ZRAM_IDLE bit for idlepage writeback in writeback

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Date:   Thu, 23 Jan 2020 10:39:36 +0800
From:   Yue Hu <zbestahu@...il.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     ngupta@...are.org, sergey.senozhatsky.work@...il.com,
        linux-kernel@...r.kernel.org, huyue2@...ong.com
Subject: Re: [PATCH] zram: do not set ZRAM_IDLE bit for idlepage writeback
 in writeback_store()

On Wed, 22 Jan 2020 18:23:05 -0800
Minchan Kim <minchan@...nel.org> wrote:

> On Tue, Jan 21, 2020 at 07:35:57PM +0800, Yue Hu wrote:
> > From: Yue Hu <huyue2@...ong.com>
> > 
> > Currently, we will call zram_set_flag() to set ZRAM_IDLE bit even for
> > idlepage writeback. That is pointless. Let's set it only for hugepage mode.  
> 
> Could you be more specific? What do you see the problem with that?

If current writeback mode is idle, ZRAM_IDLE bit will be check firstly for this
slot. Then go to call zram_set_flag(, , ZRAM_IDLE) if it's marked as ZRAM_IDLE.
So, it's duplicated setting, am i right? 

Thx.

> 
> > 
> > Signed-off-by: Yue Hu <huyue2@...ong.com>
> > ---
> >  drivers/block/zram/zram_drv.c | 12 +++++++-----
> >  1 file changed, 7 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > index 4285e75..eef5767 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -689,16 +689,18 @@ static ssize_t writeback_store(struct device *dev,
> >  		if (mode == IDLE_WRITEBACK &&
> >  			  !zram_test_flag(zram, index, ZRAM_IDLE))
> >  			goto next;
> > -		if (mode == HUGE_WRITEBACK &&
> > -			  !zram_test_flag(zram, index, ZRAM_HUGE))
> > -			goto next;
> > +		if (mode == HUGE_WRITEBACK) {
> > +			if (!zram_test_flag(zram, index, ZRAM_HUGE))
> > +				goto next;
> > +			/* Need for hugepage writeback racing */
> > +			zram_set_flag(zram, index, ZRAM_IDLE);
> > +		}
> > +
> >  		/*
> >  		 * Clearing ZRAM_UNDER_WB is duty of caller.
> >  		 * IOW, zram_free_page never clear it.
> >  		 */
> >  		zram_set_flag(zram, index, ZRAM_UNDER_WB);
> > -		/* Need for hugepage writeback racing */
> > -		zram_set_flag(zram, index, ZRAM_IDLE);
> >  		zram_slot_unlock(zram, index);
> >  		if (zram_bvec_read(zram, &bvec, index, 0, NULL)) {
> >  			zram_slot_lock(zram, index);
> > -- 
> > 1.9.1
> >