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

[Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>]

Hello Minchan,

On (03/04/15 16:06), Minchan Kim 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.

only if we talk about sizeof(struct zram), of course. we pass zram pointers around,
do struct zram loads/stores (accessing disksize, meta, writing stats, etc.) quite a
lot. so keeping it small is a good thing, I think.

	-ss

> > 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
>