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Date: Mon, 21 Jan 2013 20:39:00 +0100
From: Jerome Marchand <jmarchan@...hat.com>
To: Minchan Kim <minchan@...nel.org>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Nitin Gupta <ngupta@...are.org>,
Seth Jennings <sjenning@...ux.vnet.ibm.com>,
Konrad Rzeszutek Wilk <konrad@...nok.org>,
Dan Magenheimer <dan.magenheimer@...cle.com>,
Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH v3 1/4] zram: force disksize setting before using zram
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@...are.org>
> Acked-by: Dan Magenheimer <dan.magenheimer@...cle.com>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
> 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;
> }
>
>
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