Re: [PATCH 1/2] zram: force disksize setting before using zram

[Minchan Kim <minchan@kernel.org>]

On Mon, Nov 26, 2012 at 09:04:47PM -0800, Nitin Gupta wrote:
> On 11/22/2012 06:42 PM, 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.
> >
> >Signed-off-by: Minchan Kim <minchan@kernel.org>
> >---
> >  drivers/staging/zram/zram.txt     |    7 +++--
> >  drivers/staging/zram/zram_drv.c   |   57 ++++++++++++++-----------------------
> >  drivers/staging/zram/zram_drv.h   |    5 +---
> >  drivers/staging/zram/zram_sysfs.c |    6 +---
> >  4 files changed, 27 insertions(+), 48 deletions(-)
> >
> >diff --git a/drivers/staging/zram/zram.txt b/drivers/staging/zram/zram.txt
> >index 5f75d29..00ae66b 100644
> >--- a/drivers/staging/zram/zram.txt
> >+++ b/drivers/staging/zram/zram.txt
> >@@ -23,10 +23,9 @@ 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):
> >+2) Set Disksize
> >  	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.
> >+	(in bytes).
> >
> 
> Disksize can now be set using K/M/G suffixes also (see Sergey's
> change: handle mem suffixes in disk size ...). So, this should be
> documented as:
> 
> 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
> 

Done.

> 
> >  	# Initialize /dev/zram0 with 50MB disksize
> >  	echo $((50*1024*1024)) > /sys/block/zram0/disksize
> >@@ -67,6 +66,8 @@ Following shows a typical sequence of steps for using zram.
> >
> >  	(This frees all the memory allocated for the given device).
> >
> >+	If you want to use zram again, you should set disksize first
> >+	due to reset zram.
> 
> 
> 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.

Done.

> 
> >
> >  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 fb4a7c9..9ef1eca 100644
> >--- a/drivers/staging/zram/zram_drv.c
> >+++ b/drivers/staging/zram/zram_drv.c
> >@@ -104,35 +104,6 @@ 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
> >-		);
> >-	}
> >-
> >-	zram->disksize &= PAGE_MASK;
> >-}
> >-
> >  static void zram_free_page(struct zram *zram, size_t index)
> >  {
> >  	unsigned long handle = zram->table[index].handle;
> >@@ -497,6 +468,9 @@ void __zram_reset_device(struct zram *zram)
> >  {
> >  	size_t index;
> >
> >+	if (!zram->init_done)
> >+		goto out;
> >+
> >  	zram->init_done = 0;
> >
> >  	/* Free various per-device buffers */
> >@@ -523,8 +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)
> >@@ -540,13 +515,26 @@ int zram_init_device(struct zram *zram)
> >  	size_t num_pages;
> >
> >  	down_write(&zram->init_lock);
> >-
> >  	if (zram->init_done) {
> >  		up_write(&zram->init_lock);
> >  		return 0;
> >  	}
> >
> >-	zram_set_disksize(zram, totalram_pages << PAGE_SHIFT);
> >+	BUG_ON(!zram->disksize);
> 
> It shouldn't cause a crash if user sets disksize to zero; a noop
> seems better.

I removed it because following patch gets rid of it.
Thanks for good suggestion for document.

-- 
Kind regards,
Minchan Kim

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