linux-kernel - Re: [PATCH v1 4/5] zram: add swap full hint

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Message-ID: <20140925010738.GC17364@bbox>
Date:	Thu, 25 Sep 2014 10:07:38 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Jerome Marchand <jmarchan@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Hugh Dickins <hughd@...gle.com>, Shaohua Li <shli@...nel.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Dan Streetman <ddstreet@...e.org>,
	Nitin Gupta <ngupta@...are.org>,
	Luigi Semenzato <semenzato@...gle.com>, juno.choi@....com
Subject: Re: [PATCH v1 4/5] zram: add swap full hint

On Wed, Sep 24, 2014 at 05:10:22PM +0200, Jerome Marchand wrote:
> On 09/23/2014 11:17 PM, Andrew Morton wrote:
> > On Tue, 23 Sep 2014 13:56:02 +0900 Minchan Kim <minchan@...nel.org> wrote:
> > 
> >>>
> >>>> +#define ZRAM_FULLNESS_PERCENT 80
> >>>
> >>> We've had problems in the past where 1% is just too large an increment
> >>> for large systems.
> >>
> >> So, do you want fullness_bytes like dirty_bytes?
> > 
> > Firstly I'd like you to think about whether we're ever likely to have
> > similar granularity problems with this tunable.  If not then forget
> > about it.
> > 
> > If yes then we should do something.  I don't like the "bytes" thing
> > much because it requires that the operator know the pool size
> > beforehand, and any time that changes, the "bytes" needs hanging too. 
> > Ratios are nice but percent is too coarse.  Maybe kernel should start
> > using "ppm" for ratios, parts per million.  hrm.
> 
> An other possibility is to use decimal fractions. AFAIK, lustre fs uses
> them already for its procfs entries.

Looks good to me. If anyone doesn't have better idea or objection,
I want to approach this way.

Thanks for the hint!

> 
> > 
> >>>> @@ -711,6 +732,7 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
> >>>>  	down_write(&zram->init_lock);
> >>>>  
> >>>>  	zram->limit_pages = 0;
> >>>> +	atomic_set(&zram->alloc_fail, 0);
> >>>>  
> >>>>  	if (!init_done(zram)) {
> >>>>  		up_write(&zram->init_lock);
> >>>> @@ -944,6 +966,34 @@ static int zram_slot_free_notify(struct block_device *bdev,
> >>>>  	return 0;
> >>>>  }
> >>>>  
> >>>> +static int zram_full(struct block_device *bdev, void *arg)
> >>>
> >>> This could return a bool.  That implies that zram_swap_hint should
> >>> return bool too, but as we haven't been told what the zram_swap_hint
> >>> return value does, I'm a bit stumped.
> >>
> >> Hmm, currently, SWAP_FREE doesn't use return and SWAP_FULL uses return
> >> as bool so in the end, we can change it as bool but I want to remain it
> >> as int for the future. At least, we might use it as propagating error
> >> in future. Instead, I will use *arg to return the result instead of
> >> return val. But I'm not strong so if you want to remove return val,
> >> I will do it. For clarifictaion, please tell me again if you want.
> > 
> > I'm easy, as long as it makes sense, is understandable by people other
> > than he-who-wrote-it and doesn't use argument names such as "arg".
> > 
> > 
> 
> 



-- 
Kind regards,
Minchan Kim
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