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Date: Thu, 17 Jul 2014 23:04:40 +0900
From: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To: Timofey Titovets <nefelim4ag@...il.com>
Cc: minchan@...nel.org,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Jerome Marchand <jmarchan@...hat.com>,
Nitin Gupta <ngupta@...are.org>
Subject: Re: [PATCH v2] zram: auto add/del devices on demand
On (07/17/14 15:27), Timofey Titovets wrote:
> This add supporting of autochange count of zram devices on demand, like loop
> devices;
> This working by following rules:
> - Always save minimum devices count specified by num_device (can be
> specified while kernel module loading)
> - if last device already using add new device;
> - if last and prelast devices is free - delete last zram device;
>
> Signed-off-by: Timofey Titovets <nefelim4ag@...il.com>
>
> From v1 -> v2:
> Delete useless variable 'ret', added documentation for explain new zram
> behaviour
>
> Please pull from:
> https://github.com/Nefelim4ag/linux.git
> ---
> Tested on 3.15.5-2-ARCH, can be applied on any kernel version
> after this patch 'zram: add LZ4 compression support' - https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=6e76668e415adf799839f0ab205142ad7002d260
> ---
> diff --git a/Documentation/blockdev/zram.txt
> b/Documentation/blockdev/zram.txt
> index 0595c3f..7f5c921 100644
> --- a/Documentation/blockdev/zram.txt
> +++ b/Documentation/blockdev/zram.txt
> @@ -18,9 +18,19 @@ Following shows a typical sequence of steps for using
> zram.
>
> 1) Load Module:
> modprobe zram num_devices=4
> - This creates 4 devices: /dev/zram{0,1,2,3}
> + This pre creates 4 devices: /dev/zram{0,1,2,3}
> (num_devices parameter is optional. Default: 1)
>
> + Kernel dynamically changes number of zram devices by demand
> + (between num_devices and 31)
> + If set disk size(4) for last device
> + kernel automatically adds new zram device
> + If last two devices have zero disk size after reset(8),
> + kernel will destroy last device
> +
> + Summing up all features, comes one simple rule:
> + "The last zram device is always free for use"
I can't understand what is the real benefit?
> 2) Set max number of compression streams
> Compression backend may use up to max_comp_streams compression streams,
> thus allowing up to max_comp_streams concurrent compression operations.
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 089e72c..9b2fc89 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -42,6 +42,10 @@ static const char *default_compressor = "lzo";
>
> /* Module params (documentation at end) */
> static unsigned int num_devices = 1;
> +static unsigned int last_created_dev = 1;
> +
> +static void zram_add_dev(void);
> +static void zram_del_dev(void);
> #define ZRAM_ATTR_RO(name) \
> static ssize_t zram_attr_##name##_show(struct device *d, \
> @@ -168,6 +172,7 @@ static ssize_t comp_algorithm_store(struct device *dev,
> struct device_attribute *attr, const char *buf, size_t len)
> {
> struct zram *zram = dev_to_zram(dev);
> +
> down_write(&zram->init_lock);
> if (init_done(zram)) {
> up_write(&zram->init_lock);
> @@ -239,6 +244,7 @@ static struct zram_meta *zram_meta_alloc(u64 disksize)
> {
> size_t num_pages;
> struct zram_meta *meta = kmalloc(sizeof(*meta), GFP_KERNEL);
> +
> if (!meta)
> goto out;
>
> @@ -374,6 +380,7 @@ static int zram_bvec_read(struct zram *zram, struct
> bio_vec *bvec,
> struct page *page;
> unsigned char *user_mem, *uncmem = NULL;
> struct zram_meta *meta = zram->meta;
> +
> page = bvec->bv_page;
>
> read_lock(&meta->tb_lock);
> @@ -607,6 +614,7 @@ static void zram_reset_device(struct zram *zram, bool
> reset_capacity)
> /* Free all pages that are still in this zram device */
> for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
> unsigned long handle = meta->table[index].handle;
> +
> if (!handle)
> continue;
>
> @@ -668,6 +676,7 @@ static ssize_t disksize_store(struct device *dev,
> set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
> revalidate_disk(zram->disk);
> up_write(&zram->init_lock);
> + zram_add_dev();
> return len;
>
> out_destroy_comp:
> @@ -712,6 +721,7 @@ static ssize_t reset_store(struct device *dev,
> bdput(bdev);
>
> zram_reset_device(zram, true);
> + zram_del_dev();
> return len;
>
> out:
> @@ -954,6 +964,41 @@ static void destroy_device(struct zram *zram)
> blk_cleanup_queue(zram->queue);
> }
>
> +/* remove last free device, if last and prelast dev a free */
> +static void zram_del_dev(void)
> +{
> + if (last_created_dev < num_devices)
> + return;
> +
> + if (zram_devices[last_created_dev].disksize == 0 &&
> + zram_devices[last_created_dev-1].disksize == 0
> + ) {
racy?
> + destroy_device(&zram_devices[last_created_dev]);
> + last_created_dev--;
> + pr_info("Deleted zram%u device\n", last_created_dev);
> + }
> +}
> +
> +/* Auto add empty zram device, if last device in use */
> +static void zram_add_dev(void)
> +{
> + if (last_created_dev+1 > max_num_devices) {
> + pr_warn("Can't add zram%u, max device number reached\n",
> + num_devices);
> + return;
> + }
racy?
> + if (&zram_devices[last_created_dev].disksize > 0) {
> + last_created_dev++;
> + if (create_device(&zram_devices[last_created_dev], last_created_dev)) {
> + destroy_device(&zram_devices[last_created_dev]);
> + last_created_dev--;
racy?
-ss
> + return;
> + }
> + pr_info("Created zram%u device\n", last_created_dev);
> + }
> +}
> +
> static int __init zram_init(void)
> {
> int ret, dev_id;
> @@ -972,18 +1017,20 @@ static int __init zram_init(void)
> goto out;
> }
>
> - /* Allocate the device array and initialize each one */
> - zram_devices = kzalloc(num_devices * sizeof(struct zram), GFP_KERNEL);
> + /* Allocate the device array */
> + zram_devices = kcalloc(max_num_devices, sizeof(struct zram), GFP_KERNEL);
> if (!zram_devices) {
> ret = -ENOMEM;
> goto unregister;
> }
>
> + /* Initialise zram{0..num_devices} */
> for (dev_id = 0; dev_id < num_devices; dev_id++) {
> ret = create_device(&zram_devices[dev_id], dev_id);
> if (ret)
> goto free_devices;
> }
> + last_created_dev = num_devices-1;
>
> pr_info("Created %u device(s) ...\n", num_devices);
>
> @@ -1004,7 +1051,7 @@ static void __exit zram_exit(void)
> int i;
> struct zram *zram;
>
> - for (i = 0; i < num_devices; i++) {
> + for (i = 0; i < last_created_dev+1; i++) {
> zram = &zram_devices[i];
>
> destroy_device(zram);
> @@ -1025,7 +1072,7 @@ module_init(zram_init);
> module_exit(zram_exit);
>
> module_param(num_devices, uint, 0);
> -MODULE_PARM_DESC(num_devices, "Number of zram devices");
> +MODULE_PARM_DESC(num_devices, "Number of pre created zram devices");
>
> MODULE_LICENSE("Dual BSD/GPL");
> MODULE_AUTHOR("Nitin Gupta <ngupta@...are.org>");
>
--
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