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: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Documentation/ABI/testing/sysfs-class-zram
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24
Documentation/ABI/testing/sysfs-class-zram
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@ -0,0 +1,24 @@
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What: /sys/class/zram-control/
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Date: August 2015
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KernelVersion: 4.2
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Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
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Description:
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The zram-control/ class sub-directory belongs to zram
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device class
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What: /sys/class/zram-control/hot_add
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Date: August 2015
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KernelVersion: 4.2
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Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
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Description:
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RO attribute. Read operation will cause zram to add a new
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device and return its device id back to user (so one can
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use /dev/zram<id>), or error code.
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What: /sys/class/zram-control/hot_remove
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Date: August 2015
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KernelVersion: 4.2
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Contact: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
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Description:
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WO attribute. Remove a specific /dev/zramX device, where X
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is a device_id provided by user.
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@ -99,7 +99,24 @@ size of the disk when not in use so a huge zram is wasteful.
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mkfs.ext4 /dev/zram1
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mount /dev/zram1 /tmp
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7) Stats:
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7) Add/remove zram devices
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zram provides a control interface, which enables dynamic (on-demand) device
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addition and removal.
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In order to add a new /dev/zramX device, perform read operation on hot_add
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attribute. This will return either new device's device id (meaning that you
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can use /dev/zram<id>) or error code.
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Example:
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cat /sys/class/zram-control/hot_add
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1
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To remove the existing /dev/zramX device (where X is a device id)
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execute
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echo X > /sys/class/zram-control/hot_remove
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8) Stats:
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Per-device statistics are exported as various nodes under /sys/block/zram<id>/
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A brief description of exported device attritbutes. For more details please
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@ -174,11 +191,11 @@ line of text and contains the following stats separated by whitespace:
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zero_pages
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num_migrated
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8) Deactivate:
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9) Deactivate:
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swapoff /dev/zram0
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umount /dev/zram1
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9) Reset:
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10) Reset:
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Write any positive value to 'reset' sysfs node
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echo 1 > /sys/block/zram0/reset
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echo 1 > /sys/block/zram1/reset
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@ -29,10 +29,14 @@
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#include <linux/vmalloc.h>
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#include <linux/err.h>
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#include <linux/idr.h>
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#include <linux/sysfs.h>
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#include "zram_drv.h"
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static DEFINE_IDR(zram_index_idr);
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/* idr index must be protected */
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static DEFINE_MUTEX(zram_index_mutex);
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static int zram_major;
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static const char *default_compressor = "lzo";
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@ -1273,24 +1277,104 @@ out_free_dev:
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return ret;
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}
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static void zram_remove(struct zram *zram)
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static int zram_remove(struct zram *zram)
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{
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pr_info("Removed device: %s\n", zram->disk->disk_name);
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struct block_device *bdev;
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bdev = bdget_disk(zram->disk, 0);
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if (!bdev)
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return -ENOMEM;
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mutex_lock(&bdev->bd_mutex);
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if (bdev->bd_openers || zram->claim) {
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mutex_unlock(&bdev->bd_mutex);
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bdput(bdev);
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return -EBUSY;
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}
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zram->claim = true;
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mutex_unlock(&bdev->bd_mutex);
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/*
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* Remove sysfs first, so no one will perform a disksize
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* store while we destroy the devices
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* store while we destroy the devices. This also helps during
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* hot_remove -- zram_reset_device() is the last holder of
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* ->init_lock, no later/concurrent disksize_store() or any
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* other sysfs handlers are possible.
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*/
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sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
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&zram_disk_attr_group);
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/* Make sure all the pending I/O are finished */
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fsync_bdev(bdev);
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zram_reset_device(zram);
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bdput(bdev);
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pr_info("Removed device: %s\n", zram->disk->disk_name);
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idr_remove(&zram_index_idr, zram->disk->first_minor);
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blk_cleanup_queue(zram->disk->queue);
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del_gendisk(zram->disk);
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put_disk(zram->disk);
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kfree(zram);
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return 0;
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}
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/* zram-control sysfs attributes */
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static ssize_t hot_add_show(struct class *class,
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struct class_attribute *attr,
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char *buf)
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{
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int ret;
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mutex_lock(&zram_index_mutex);
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ret = zram_add();
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mutex_unlock(&zram_index_mutex);
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if (ret < 0)
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return ret;
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return scnprintf(buf, PAGE_SIZE, "%d\n", ret);
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}
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static ssize_t hot_remove_store(struct class *class,
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struct class_attribute *attr,
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const char *buf,
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size_t count)
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{
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struct zram *zram;
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int ret, dev_id;
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/* dev_id is gendisk->first_minor, which is `int' */
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ret = kstrtoint(buf, 10, &dev_id);
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if (ret)
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return ret;
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if (dev_id < 0)
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return -EINVAL;
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mutex_lock(&zram_index_mutex);
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zram = idr_find(&zram_index_idr, dev_id);
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if (zram)
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ret = zram_remove(zram);
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else
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ret = -ENODEV;
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mutex_unlock(&zram_index_mutex);
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return ret ? ret : count;
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}
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static struct class_attribute zram_control_class_attrs[] = {
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__ATTR_RO(hot_add),
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__ATTR_WO(hot_remove),
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__ATTR_NULL,
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};
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static struct class zram_control_class = {
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.name = "zram-control",
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.owner = THIS_MODULE,
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.class_attrs = zram_control_class_attrs,
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};
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static int zram_remove_cb(int id, void *ptr, void *data)
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{
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zram_remove(ptr);
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static void destroy_devices(void)
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{
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class_unregister(&zram_control_class);
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idr_for_each(&zram_index_idr, &zram_remove_cb, NULL);
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idr_destroy(&zram_index_idr);
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unregister_blkdev(zram_major, "zram");
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{
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int ret;
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ret = class_register(&zram_control_class);
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if (ret) {
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pr_warn("Unable to register zram-control class\n");
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return ret;
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}
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zram_major = register_blkdev(0, "zram");
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if (zram_major <= 0) {
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pr_warn("Unable to get major number\n");
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class_unregister(&zram_control_class);
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return -EBUSY;
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}
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while (num_devices != 0) {
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mutex_lock(&zram_index_mutex);
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ret = zram_add();
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mutex_unlock(&zram_index_mutex);
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if (ret < 0)
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goto out_error;
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num_devices--;
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