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

[Minchan Kim <minchan@kernel.org>]

On Wed, Mar 04, 2015 at 04:49:13PM +0900, Sergey Senozhatsky wrote:
> On (03/04/15 16:06), Minchan Kim wrote:
> > 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.
> > 
> 
> and idr handles auto device_id generation for us, all we need to do in zram code
> is to pass '0, 0' to idr_alloc(), instead of 'device_id, device_id + 1'.
> hoping that automatic id generation will be there one day.

About memory footprint, sizeof(list_head) might be win if we create zram dyamically
and there is few zram device in the system because IDR uses own metadata and bitmap
and so. But I don't think it's not too much if there is few device, either.
However, automatic id generation appeals more rather than memory footprint so I hope
you add it in description for someone to know why we decided idr in future.

Thanks.

> 
> 	-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
> > 

-- 
Kind regards,
Minchan Kim