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Message-ID: <50B449EF.50806@vflare.org>
Date: Mon, 26 Nov 2012 21:04:47 -0800
From: Nitin Gupta <ngupta@...are.org>
To: Minchan Kim <minchan@...nel.org>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Seth Jennings <sjenning@...ux.vnet.ibm.com>,
Jerome Marchand <jmarchan@...hat.com>,
Dan Magenheimer <dan.magenheimer@...cle.com>,
Konrad Rzeszutek Wilk <konrad@...nok.org>,
Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 1/2] zram: force disksize setting before using zram
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@...nel.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
> # 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.
>
> 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.
Thanks,
Nitin
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