Re: [PATCH v3 1/4] zram: force disksize setting before using zram

[Jerome Marchand]

On 01/21/2013 06:21 AM, Minchan Kim wrote:
> Now zram document syas "set disksize is optional"
> but partly it's wrong. When you try to use zram firstly after
> booting, you must set disksize, otherwise zram can't work because
> zram gendisk's size is 0. But once you do it, you can use zram freely
> after reset because reset doesn't reset to zero paradoxically.
> So in this time, disksize setting is optional.:(
> It's inconsitent for user behavior and not straightforward.
> 
> This patch forces always setting disksize firstly before using zram.
> Yes. It changes current behavior so someone could complain when
> he upgrades zram. Apparently it could be a problem if zram is mainline
> but it still lives in staging so behavior could be changed for right
> way to go. Let them excuse.
> 
> Cc: Nitin Gupta <ngupta@xxxxxxxxxx>
> Acked-by: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
>  drivers/staging/zram/zram.txt     |   27 +++++++++----------
>  drivers/staging/zram/zram_drv.c   |   52 ++++++++++++++-----------------------
>  drivers/staging/zram/zram_drv.h   |    5 +---
>  drivers/staging/zram/zram_sysfs.c |    6 +----
>  4 files changed, 35 insertions(+), 55 deletions(-)
> 
> diff --git a/drivers/staging/zram/zram.txt b/drivers/staging/zram/zram.txt
> index 5f75d29..765d790 100644
> --- a/drivers/staging/zram/zram.txt
> +++ b/drivers/staging/zram/zram.txt
> @@ -23,17 +23,17 @@ Following shows a typical sequence of steps for using zram.
>  	This creates 4 devices: /dev/zram{0,1,2,3}
>  	(num_devices parameter is optional. Default: 1)
>  
> -2) Set Disksize (Optional):
> -	Set disk size by writing the value to sysfs node 'disksize'
> -	(in bytes). If disksize is not given, default value of 25%
> -	of RAM is used.
> -
> -	# Initialize /dev/zram0 with 50MB disksize
> -	echo $((50*1024*1024)) > /sys/block/zram0/disksize
> -
> -	NOTE: disksize cannot be changed if the disk contains any
> -	data. So, for such a disk, you need to issue 'reset' (see below)
> -	before you can change its disksize.
> +2) Set Disksize
> +        Set disk size by writing the value to sysfs node 'disksize'.
> +        The value can be either in bytes or you can use mem suffixes.
> +        Examples:
> +            # Initialize /dev/zram0 with 50MB disksize
> +            echo $((50*1024*1024)) > /sys/block/zram0/disksize
> +
> +            # Using mem suffixes
> +            echo 256K > /sys/block/zram0/disksize
> +            echo 512M > /sys/block/zram0/disksize
> +            echo 1G > /sys/block/zram0/disksize
>  
>  3) Activate:
>  	mkswap /dev/zram0
> @@ -65,8 +65,9 @@ Following shows a typical sequence of steps for using zram.
>  	echo 1 > /sys/block/zram0/reset
>  	echo 1 > /sys/block/zram1/reset
>  
> -	(This frees all the memory allocated for the given device).
> -
> +	This frees all the memory allocated for the given device and
> +	resets the disksize to zero. You must set the disksize again
> +	before reusing the device.
>  
>  Please report any problems at:
>   - Mailing list: linux-mm-cc at laptop dot org
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index 61fb8f1..1d45401 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -94,34 +94,6 @@ static int page_zero_filled(void *ptr)
>  	return 1;
>  }
>  
> -static void zram_set_disksize(struct zram *zram, size_t totalram_bytes)
> -{
> -	if (!zram->disksize) {
> -		pr_info(
> -		"disk size not provided. You can use disksize_kb module "
> -		"param to specify size.\nUsing default: (%u%% of RAM).\n",
> -		default_disksize_perc_ram
> -		);
> -		zram->disksize = default_disksize_perc_ram *
> -					(totalram_bytes / 100);
> -	}
> -
> -	if (zram->disksize > 2 * (totalram_bytes)) {
> -		pr_info(
> -		"There is little point creating a zram of greater than "
> -		"twice the size of memory since we expect a 2:1 compression "
> -		"ratio. Note that zram uses about 0.1%% of the size of "
> -		"the disk when not in use so a huge zram is "
> -		"wasteful.\n"
> -		"\tMemory Size: %zu kB\n"
> -		"\tSize you selected: %llu kB\n"
> -		"Continuing anyway ...\n",
> -		totalram_bytes >> 10, zram->disksize >> 10);
> -	}
> -
> -	zram->disksize &= PAGE_MASK;
> -}
> -
>  static void zram_free_page(struct zram *zram, size_t index)
>  {
>  	unsigned long handle = zram->table[index].handle;
> @@ -495,6 +467,9 @@ void __zram_reset_device(struct zram *zram)
>  {
>  	size_t index;
>  
> +	if (!zram->init_done)
> +		goto out;

In that case, the device has not been initialized yet or has been
reset already. zram->disksize and disk capacity should already been
zero in that case. Why don't we just return here?

Jerome

> +
>  	zram->init_done = 0;
>  
>  	/* Free various per-device buffers */
> @@ -522,7 +497,9 @@ void __zram_reset_device(struct zram *zram)
>  	/* Reset stats */
>  	memset(&zram->stats, 0, sizeof(zram->stats));
>  
> +out:
>  	zram->disksize = 0;
> +	set_capacity(zram->disk, 0);
>  }
>  
>  void zram_reset_device(struct zram *zram)
> @@ -544,7 +521,19 @@ int zram_init_device(struct zram *zram)
>  		return 0;
>  	}
>  
> -	zram_set_disksize(zram, totalram_pages << PAGE_SHIFT);
> +	if (zram->disksize > 2 * (totalram_pages << PAGE_SHIFT)) {
> +		pr_info(
> +		"There is little point creating a zram of greater than "
> +		"twice the size of memory since we expect a 2:1 compression "
> +		"ratio. Note that zram uses about 0.1%% of the size of "
> +		"the disk when not in use so a huge zram is "
> +		"wasteful.\n"
> +		"\tMemory Size: %zu kB\n"
> +		"\tSize you selected: %llu kB\n"
> +		"Continuing anyway ...\n",
> +		(totalram_pages << PAGE_SHIFT) >> 10, zram->disksize >> 10
> +		);
> +	}
>  
>  	zram->compress_workmem = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
>  	if (!zram->compress_workmem) {
> @@ -569,8 +558,6 @@ int zram_init_device(struct zram *zram)
>  		goto fail_no_table;
>  	}
>  
> -	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
> -
>  	/* zram devices sort of resembles non-rotational disks */
>  	queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);
>  
> @@ -749,8 +736,7 @@ static void __exit zram_exit(void)
>  		zram = &zram_devices[i];
>  
>  		destroy_device(zram);
> -		if (zram->init_done)
> -			zram_reset_device(zram);
> +		zram_reset_device(zram);
>  	}
>  
>  	unregister_blkdev(zram_major, "zram");
> diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
> index df2eec4..5b671d1 100644
> --- a/drivers/staging/zram/zram_drv.h
> +++ b/drivers/staging/zram/zram_drv.h
> @@ -28,9 +28,6 @@ static const unsigned max_num_devices = 32;
>  
>  /*-- Configurable parameters */
>  
> -/* Default zram disk size: 25% of total RAM */
> -static const unsigned default_disksize_perc_ram = 25;
> -
>  /*
>   * Pages that compress to size greater than this are stored
>   * uncompressed in memory.
> @@ -115,6 +112,6 @@ extern struct attribute_group zram_disk_attr_group;
>  #endif
>  
>  extern int zram_init_device(struct zram *zram);
> -extern void __zram_reset_device(struct zram *zram);
> +extern void zram_reset_device(struct zram *zram);
>  
>  #endif
> diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c
> index de1eacf..4143af9 100644
> --- a/drivers/staging/zram/zram_sysfs.c
> +++ b/drivers/staging/zram/zram_sysfs.c
> @@ -110,11 +110,7 @@ static ssize_t reset_store(struct device *dev,
>  	if (bdev)
>  		fsync_bdev(bdev);
>  
> -	down_write(&zram->init_lock);
> -	if (zram->init_done)
> -		__zram_reset_device(zram);
> -	up_write(&zram->init_lock);
> -
> +	zram_reset_device(zram);
>  	return len;
>  }
>  
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/