linux-kernel - Re: [PATCH v3 3/3] zram: implement rw

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Date:	Wed, 22 Oct 2014 10:28:57 +0900
From:	"karam.lee" <karam.lee@....com>
To:	Jerome Marchand <jmarchan@...hat.com>
Cc:	minchan@...nel.org, ngupta@...are.org,
	linux-kernel@...r.kernel.org, matthew.r.wilcox@...el.com,
	seungho1.park@....com
Subject: Re: [PATCH v3 3/3] zram: implement rw_page operation of zram

On Tue, Oct 21, 2014 at 03:57:29PM +0200, Jerome Marchand wrote:
> On 10/21/2014 09:27 AM, karam.lee@....com wrote:
> > From: "karam.lee" <karam.lee@....com>
> > 
> > This patch implements rw_page operation for zram block device.
> > 
> > I implemented the feature in zram and tested it.
> > Test bed was the G2, LG electronic mobile device, whtich has msm8974
> > processor and 2GB memory.
> > With a memory allocation test program consuming memory, the system
> > generates swap.
> > And operating time of swap_write_page() was measured.
> > 
> > --------------------------------------------------
> > |             |   operating time   | improvement |
> > |             |  (20 runs average) |             |
> > --------------------------------------------------
> > |with patch   |    1061.15 us      |    +2.4%    |
> > --------------------------------------------------
> > |without patch|    1087.35 us      |             |
> > --------------------------------------------------
> > 
> > Each test(with paged_io,with BIO) result set shows normal distribution
> > and has equal variance.
> > I mean the two values are valid result to compare.
> > I can say operation with paged I/O(without BIO) is faster 2.4% with
> > confidence level 95%.
> > 
> > Signed-off-by: karam.lee <karam.lee@....com>
> > ---
> >  drivers/block/zram/zram_drv.c |   38 ++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 38 insertions(+)
> > 
> > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > index 4565fdc..696f0b5 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -810,8 +810,46 @@ static void zram_slot_free_notify(struct block_device *bdev,
> >  	atomic64_inc(&zram->stats.notify_free);
> >  }
> >  
> > +static int zram_rw_page(struct block_device *bdev, sector_t sector,
> > +		       struct page *page, int rw)
> > +{
> > +	int offset, ret = 1;
> 
> Small nitpick, but why do you initialize ret to 1? It doesn't seem to be
> ever used (nor is 1 a valid return value AFAICT).
> 
> It otherwise looks good.
> 
> Acked-by: Jerome Marchand <jmarchan@...hat.com>
> 

Thank you for reply. I agree with your opinion.

It was my mistake to initialize ret to 1.

I will resend the fixed version.

> > +	u32 index;
> > +	struct zram *zram;
> > +	struct bio_vec bv;
> > +
> > +	zram = bdev->bd_disk->private_data;
> > +	if (!valid_io_request(zram, sector, PAGE_SIZE)) {
> > +		atomic64_inc(&zram->stats.invalid_io);
> > +		ret = -EINVAL;
> > +		goto out;
> > +	}
> > +
> > +	down_read(&zram->init_lock);
> > +	if (unlikely(!init_done(zram))) {
> > +		ret = -ENOMEM;
> > +		goto out_unlock;
> > +	}
> > +
> > +	index = sector >> SECTORS_PER_PAGE_SHIFT;
> > +	offset = sector & (SECTORS_PER_PAGE - 1) << SECTOR_SHIFT;
> > +
> > +	bv.bv_page = page;
> > +	bv.bv_len = PAGE_SIZE;
> > +	bv.bv_offset = 0;
> > +
> > +	ret = zram_bvec_rw(zram, &bv, index, offset, rw);
> > +
> > +out_unlock:
> > +	up_read(&zram->init_lock);
> > +out:
> > +	page_endio(page, rw, ret);
> > +	return ret;
> > +}
> > +
> >  static const struct block_device_operations zram_devops = {
> >  	.swap_slot_free_notify = zram_slot_free_notify,
> > +	.rw_page = zram_rw_page,
> >  	.owner = THIS_MODULE
> >  };
> >  
> > 
> 
> 


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