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Commit 6566d1a3 authored by Sergey Senozhatsky's avatar Sergey Senozhatsky Committed by Linus Torvalds
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zram: add dynamic device add/remove functionality 



We currently don't support on-demand device creation.  The one and only
way to have N zram devices is to specify num_devices module parameter
(default value: 1).  IOW if, for some reason, at some point, user wants
to have N + 1 devies he/she must umount all the existing devices, unload
the module, load the module passing num_devices equals to N + 1.  And do
this again, if needed.

This patch introduces zram control sysfs class, which has two sysfs
attrs:
- hot_add      -- add a new zram device
- hot_remove   -- remove a specific (device_id) zram device

hot_add sysfs attr is read-only and has only automatic device id
assignment mode (as requested by Minchan Kim).  read operation performed
on this attr creates a new zram device and returns back its device_id or
error status.

Usage example:
	# add a new specific zram device
	cat /sys/class/zram-control/hot_add
	2

	# remove a specific zram device
	echo 4 > /sys/class/zram-control/hot_remove

Returning zram_add() error code back to user (-ENOMEM in this case)

	cat /sys/class/zram-control/hot_add
	cat: /sys/class/zram-control/hot_add: Cannot allocate memory

NOTE, there might be users who already depend on the fact that at least
zram0 device gets always created by zram_init(). Preserve this behavior.

[minchan@kernel.org: use zram->claim to avoid lockdep splat]
Signed-off-by: default avatarSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f405c445

Documentation/ABI/testing/sysfs-class-zram

0 → 100644
+24 −0
Original line number Diff line number Diff line 
What:		/sys/class/zram-control/

Date:		August 2015

KernelVersion:	4.2

Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

Description:

		The zram-control/ class sub-directory belongs to zram

		device class



What:		/sys/class/zram-control/hot_add

Date:		August 2015

KernelVersion:	4.2

Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

Description:

		RO attribute. Read operation will cause zram to add a new

		device and return its device id back to user (so one can

		use /dev/zram<id>), or error code.



What:		/sys/class/zram-control/hot_remove

Date:		August 2015

KernelVersion:	4.2

Contact:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

Description:

		WO attribute. Remove a specific /dev/zramX device, where X

		is a device_id provided by user.

Documentation/blockdev/zram.txt

+20 −3
Original line number Diff line number Diff line
@@ -99,7 +99,24 @@ size of the disk when not in use so a huge zram is wasteful. 
	mkfs.ext4 /dev/zram1

	mount /dev/zram1 /tmp



7) Stats:

7) Add/remove zram devices



zram provides a control interface, which enables dynamic (on-demand) device

addition and removal.



In order to add a new /dev/zramX device, perform read operation on hot_add

attribute. This will return either new device's device id (meaning that you

can use /dev/zram<id>) or error code.



Example:

	cat /sys/class/zram-control/hot_add

	1



To remove the existing /dev/zramX device (where X is a device id)

execute

	echo X > /sys/class/zram-control/hot_remove



8) Stats:

Per-device statistics are exported as various nodes under /sys/block/zram<id>/



A brief description of exported device attritbutes. For more details please
@@ -174,11 +191,11 @@ line of text and contains the following stats separated by whitespace: 
	zero_pages

	num_migrated



8) Deactivate:

9) Deactivate:

	swapoff /dev/zram0

	umount /dev/zram1



9) Reset:

10) Reset:

	Write any positive value to 'reset' sysfs node

	echo 1 > /sys/block/zram0/reset

	echo 1 > /sys/block/zram1/reset

drivers/block/zram/zram_drv.c

+97 −3
Original line number Diff line number Diff line
@@ -29,10 +29,14 @@ 
#include <linux/vmalloc.h>

#include <linux/err.h>

#include <linux/idr.h>

#include <linux/sysfs.h>



#include "zram_drv.h"



static DEFINE_IDR(zram_index_idr);

/* idr index must be protected */

static DEFINE_MUTEX(zram_index_mutex);



static int zram_major;

static const char *default_compressor = "lzo";
@@ -1273,24 +1277,104 @@ static int zram_add(void) 
	return ret;

}



static void zram_remove(struct zram *zram)

static int zram_remove(struct zram *zram)

{

	pr_info("Removed device: %s\n", zram->disk->disk_name);

	struct block_device *bdev;



	bdev = bdget_disk(zram->disk, 0);

	if (!bdev)

		return -ENOMEM;



	mutex_lock(&bdev->bd_mutex);

	if (bdev->bd_openers || zram->claim) {

		mutex_unlock(&bdev->bd_mutex);

		bdput(bdev);

		return -EBUSY;

	}



	zram->claim = true;

	mutex_unlock(&bdev->bd_mutex);



	/*

	 * Remove sysfs first, so no one will perform a disksize

	 * store while we destroy the devices

	 * store while we destroy the devices. This also helps during

	 * hot_remove -- zram_reset_device() is the last holder of

	 * ->init_lock, no later/concurrent disksize_store() or any

	 * other sysfs handlers are possible.

	 */

	sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,

			&zram_disk_attr_group);



	/* Make sure all the pending I/O are finished */

	fsync_bdev(bdev);

	zram_reset_device(zram);

	bdput(bdev);



	pr_info("Removed device: %s\n", zram->disk->disk_name);



	idr_remove(&zram_index_idr, zram->disk->first_minor);

	blk_cleanup_queue(zram->disk->queue);

	del_gendisk(zram->disk);

	put_disk(zram->disk);

	kfree(zram);

	return 0;

}



/* zram-control sysfs attributes */

static ssize_t hot_add_show(struct class *class,

			struct class_attribute *attr,

			char *buf)

{

	int ret;



	mutex_lock(&zram_index_mutex);

	ret = zram_add();

	mutex_unlock(&zram_index_mutex);



	if (ret < 0)

		return ret;

	return scnprintf(buf, PAGE_SIZE, "%d\n", ret);

}



static ssize_t hot_remove_store(struct class *class,

			struct class_attribute *attr,

			const char *buf,

			size_t count)

{

	struct zram *zram;

	int ret, dev_id;



	/* dev_id is gendisk->first_minor, which is `int' */

	ret = kstrtoint(buf, 10, &dev_id);

	if (ret)

		return ret;

	if (dev_id < 0)

		return -EINVAL;



	mutex_lock(&zram_index_mutex);



	zram = idr_find(&zram_index_idr, dev_id);

	if (zram)

		ret = zram_remove(zram);

	else

		ret = -ENODEV;



	mutex_unlock(&zram_index_mutex);

	return ret ? ret : count;

}



static struct class_attribute zram_control_class_attrs[] = {

	__ATTR_RO(hot_add),

	__ATTR_WO(hot_remove),

	__ATTR_NULL,

};



static struct class zram_control_class = {

	.name		= "zram-control",

	.owner		= THIS_MODULE,

	.class_attrs	= zram_control_class_attrs,

};



static int zram_remove_cb(int id, void *ptr, void *data)

{

	zram_remove(ptr);
@@ -1299,6 +1383,7 @@ static int zram_remove_cb(int id, void *ptr, void *data) 


static void destroy_devices(void)

{

	class_unregister(&zram_control_class);

	idr_for_each(&zram_index_idr, &zram_remove_cb, NULL);

	idr_destroy(&zram_index_idr);

	unregister_blkdev(zram_major, "zram");
@@ -1308,14 +1393,23 @@ static int __init zram_init(void) 
{

	int ret;



	ret = class_register(&zram_control_class);

	if (ret) {

		pr_warn("Unable to register zram-control class\n");

		return ret;

	}



	zram_major = register_blkdev(0, "zram");

	if (zram_major <= 0) {

		pr_warn("Unable to get major number\n");

		class_unregister(&zram_control_class);

		return -EBUSY;

	}



	while (num_devices != 0) {

		mutex_lock(&zram_index_mutex);

		ret = zram_add();

		mutex_unlock(&zram_index_mutex);

		if (ret < 0)

			goto out_error;

		num_devices--;