Re: [PATCH 2/8] zram: use idr instead of `zram_devices' array

[Minchan Kim <minchan@kernel.org>]

Hello Sergey,

Sorry for the late review.
I don't grab a time to review in detail still but I saw Andrew merged it
to mmotm today so at least I should ask somethings now and hope review
in detail soon.

On Tue, Mar 03, 2015 at 09:49:44PM +0900, Sergey Senozhatsky wrote:
> This patch makes some preparations for dynamic device ADD/REMOVE functionality
> via /dev/zram-control interface.
> 
> Remove `zram_devices' array and switch to id-to-pointer translation (idr).
> idr doesn't bloat zram struct with additional members, f.e. list_head, yet

So are you claiming using of idr is smaller memory footprint than zram included
list_head?
I hope why you want to use idr for dynamic device management.

> still provides ability to match the device_id with the device pointer.
> No user-space visible changes.
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> ---
>  drivers/block/zram/zram_drv.c | 81 ++++++++++++++++++++++++-------------------
>  1 file changed, 46 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 8fc2566..6707b7b 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -32,12 +32,12 @@
>  #include <linux/string.h>
>  #include <linux/vmalloc.h>
>  #include <linux/err.h>
> +#include <linux/idr.h>
>  
>  #include "zram_drv.h"
>  
> -/* Globals */
> +static DEFINE_IDR(zram_index_idr);
>  static int zram_major;
> -static struct zram *zram_devices;
>  static const char *default_compressor = "lzo";
>  
>  /* Module params (documentation at end) */
> @@ -1061,18 +1061,28 @@ static struct attribute_group zram_disk_attr_group = {
>  	.attrs = zram_disk_attrs,
>  };
>  
> -static int create_device(struct zram *zram, int device_id)
> +static int zram_add(int device_id)
>  {
> +	struct zram *zram;
>  	struct request_queue *queue;
>  	int ret = -ENOMEM;
>  
> +	zram = kzalloc(sizeof(struct zram), GFP_KERNEL);
> +	if (!zram)
> +		return ret;
> +
> +	ret = idr_alloc(&zram_index_idr, zram, device_id,
> +			device_id + 1, GFP_KERNEL);
> +	if (ret < 0)
> +		goto out_free_dev;
> +
>  	init_rwsem(&zram->init_lock);
>  
>  	queue = blk_alloc_queue(GFP_KERNEL);
>  	if (!queue) {
>  		pr_err("Error allocating disk queue for device %d\n",
>  			device_id);
> -		goto out;
> +		goto out_free_idr;
>  	}
>  
>  	blk_queue_make_request(queue, zram_make_request);
> @@ -1141,34 +1151,42 @@ out_free_disk:
>  	put_disk(zram->disk);
>  out_free_queue:
>  	blk_cleanup_queue(queue);
> -out:
> +out_free_idr:
> +	idr_remove(&zram_index_idr, device_id);
> +out_free_dev:
> +	kfree(zram);
>  	return ret;
>  }
>  
> -static void destroy_devices(unsigned int nr)
> +static void zram_remove(struct zram *zram)
>  {
> -	struct zram *zram;
> -	unsigned int i;
> -
> -	for (i = 0; i < nr; i++) {
> -		zram = &zram_devices[i];
> -		/*
> -		 * Remove sysfs first, so no one will perform a disksize
> -		 * store while we destroy the devices
> -		 */
> -		sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
> -				&zram_disk_attr_group);
> +	/*
> +	 * Remove sysfs first, so no one will perform a disksize
> +	 * store while we destroy the devices
> +	 */
> +	sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
> +			&zram_disk_attr_group);
>  
> -		zram_reset_device(zram);
> +	zram_reset_device(zram);
> +	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);
> +}
>  
> -		blk_cleanup_queue(zram->disk->queue);
> -		del_gendisk(zram->disk);
> -		put_disk(zram->disk);
> -	}
> +static int zram_exit_cb(int id, void *ptr, void *data)
> +{
> +	zram_remove(ptr);
> +	return 0;
> +}
>  
> -	kfree(zram_devices);
> +static void destroy_devices(void)
> +{
> +	idr_for_each(&zram_index_idr, &zram_exit_cb, NULL);
> +	idr_destroy(&zram_index_idr);
>  	unregister_blkdev(zram_major, "zram");
> -	pr_info("Destroyed %u device(s)\n", nr);
> +	pr_info("Destroyed device(s)\n");
>  }
>  
>  static int __init zram_init(void)
> @@ -1187,16 +1205,9 @@ static int __init zram_init(void)
>  		return -EBUSY;
>  	}
>  
> -	/* Allocate the device array and initialize each one */
> -	zram_devices = kzalloc(num_devices * sizeof(struct zram), GFP_KERNEL);
> -	if (!zram_devices) {
> -		unregister_blkdev(zram_major, "zram");
> -		return -ENOMEM;
> -	}
> -
>  	for (dev_id = 0; dev_id < num_devices; dev_id++) {
> -		ret = create_device(&zram_devices[dev_id], dev_id);
> -		if (ret)
> +		ret = zram_add(dev_id);
> +		if (ret != 0)
>  			goto out_error;
>  	}
>  
> @@ -1204,13 +1215,13 @@ static int __init zram_init(void)
>  	return 0;
>  
>  out_error:
> -	destroy_devices(dev_id);
> +	destroy_devices();
>  	return ret;
>  }
>  
>  static void __exit zram_exit(void)
>  {
> -	destroy_devices(num_devices);
> +	destroy_devices();
>  }
>  
>  module_init(zram_init);
> -- 
> 2.3.1.167.g7f4ba4b
> 

-- 
Kind regards,
Minchan Kim