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

Minchan Kim
2015-03-04T07:06:36Z

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