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

Minchan Kim
2015-03-05T00:59:11Z

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