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From: Minchan Kim <minchan@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Hugh Dickins <hughd@google.com>, Shaohua Li <shli@kernel.org>,
	Jerome Marchand <jmarchan@redhat.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Dan Streetman <ddstreet@ieee.org>,
	Nitin Gupta <ngupta@vflare.org>,
	Luigi Semenzato <semenzato@google.com>,
	juno.choi@lge.com
Subject: Re: [PATCH v1 4/5] zram: add swap full hint
Date: Wed, 24 Sep 2014 16:57:12 +0900	[thread overview]
Message-ID: <20140924075712.GA3181@bbox> (raw)
In-Reply-To: <20140923141755.b7854bae484cfe434797be02@linux-foundation.org>

On Tue, Sep 23, 2014 at 02:17:55PM -0700, Andrew Morton wrote:
> On Tue, 23 Sep 2014 13:56:02 +0900 Minchan Kim <minchan@kernel.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.

When I think the usecase for zram-swap, it is used for small memory
but not sure because these days, mobile phone DRAM size tend to be
big(ex, 3G) and they want to use zRAM for swap due to wear-leveling
of nand. When I consier the trend, they might set zram-swap to about
500M in future. In that case, 1% is 5M and given zram comp ratio(ie,
max 5:1), it could be 25M which is never small for the application.
So, IMO, we need more fine-grained knob.

> 
> 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.

Okay, I will consider it more in next spin.

> 
> > > > @@ -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".

Yeb.

-- 
Kind regards,
Minchan Kim

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  reply	other threads:[~2014-09-24  7:56 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-22  0:03 [PATCH v1 0/5] stop anon reclaim when zram is full Minchan Kim
2014-09-22  0:03 ` [PATCH v1 1/5] zram: generalize swap_slot_free_notify Minchan Kim
2014-09-22 20:41   ` Andrew Morton
2014-09-23  4:45     ` Minchan Kim
2014-09-22  0:03 ` [PATCH v1 2/5] mm: add full variable in swap_info_struct Minchan Kim
2014-09-22 20:45   ` Andrew Morton
2014-09-23  4:45     ` Minchan Kim
2014-09-24  2:53   ` Dan Streetman
2014-09-24  7:57     ` Minchan Kim
2014-09-22  0:03 ` [PATCH v1 3/5] mm: VM can be aware of zram fullness Minchan Kim
2014-09-24 14:12   ` Dan Streetman
2014-09-25  1:06     ` Minchan Kim
2014-09-25  1:31       ` Dan Streetman
2014-09-22  0:03 ` [PATCH v1 4/5] zram: add swap full hint Minchan Kim
2014-09-22 21:11   ` Andrew Morton
2014-09-23  4:56     ` Minchan Kim
2014-09-23 21:17       ` Andrew Morton
2014-09-24  7:57         ` Minchan Kim [this message]
2014-09-24 15:10         ` Jerome Marchand
2014-09-25  1:07           ` Minchan Kim
2014-09-24 14:01   ` Dan Streetman
2014-09-25  1:02     ` Minchan Kim
2014-09-25 15:52       ` Dan Streetman
2014-10-06 23:36         ` Minchan Kim
2014-10-06 23:46           ` Minchan Kim
2014-10-08 18:29             ` Dan Streetman
2014-09-22  0:03 ` [PATCH v1 5/5] zram: add fullness knob to control swap full Minchan Kim
2014-09-22 21:17   ` Andrew Morton
2014-09-23  4:57     ` Minchan Kim
2014-12-02  3:04 ` [PATCH v1 0/5] stop anon reclaim when zram is full Minchan Kim

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