Re: [PATCH v3 3/3] zram: implement rw_page operation of zram

[Jerome Marchand]

On 10/21/2014 09:27 AM, karam.lee@xxxxxxx wrote:
> From: "karam.lee" <karam.lee@xxxxxxx>
> 
> 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@xxxxxxx>
> ---
>  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@xxxxxxxxxx>

> +	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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