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Message-ID: <20140729030021.GA22707@bbox>
Date: Tue, 29 Jul 2014 12:00:21 +0900
From: Minchan Kim <minchan@...nel.org>
To: Timofey Titovets <nefelim4ag@...il.com>
Cc: 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 v3 RESEND] zram: auto add new devices on demand
Hello Timofey,
Sorry for late response and thanks for suggesting new feature.
First of all, I'd like to know your usecase.
I don't mean I am against this feature and I tend to agree it would
be good if we can make new device dynamically but until now, I don't
hear any requirement like that. So we need compelling usecase to
justify maintainance overhead.
On Mon, Jul 21, 2014 at 01:46:14PM +0300, Timofey Titovets wrote:
> From: Timofey Titovets <nefelim4ag@...il.com>
>
> This add supporting of auto allocate new zram devices on demand,
> like loop devices
>
> This working by following rules:
> - Pre create zram devices specified by num_device
> - if all device already in use -> add new free device
>
> From v1 -> v2:
> Delete useless variable 'ret', added documentation for explain new
> zram behavior
>
> From v2 -> v3
> Delete logic to destroy not used devices, for avoid concurrency issues
> Code refactoring for made patch small and clean as possible
> Patch can pass the test:
>
> #!/bin/sh
> modprobe zram
> while true; do
> echo 10485760 > /sys/block/zram0/disksize&
> echo 1 > /sys/block/zram0/reset&
> done
>
> Can be pulled 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..a090ac7 100644
> --- a/Documentation/blockdev/zram.txt
> +++ b/Documentation/blockdev/zram.txt
> @@ -21,6 +21,9 @@ Following shows a typical sequence of steps for
> using zram.
> This creates 4 devices: /dev/zram{0,1,2,3}
> (num_devices parameter is optional. Default: 1)
>
> + If all device in use kernel will create new zram device
> + (between num_devices and 31)
> +
> 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..cc78779 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -43,6 +43,8 @@ static const char *default_compressor = "lzo";
> /* Module params (documentation at end) */
> static unsigned int num_devices = 1;
>
> +static inline int zram_add_dev(void);
> +
> #define ZRAM_ATTR_RO(name) \
> static ssize_t zram_attr_##name##_show(struct device *d, \
> struct device_attribute *attr, char *b) \
> @@ -168,6 +170,7 @@ 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);
> +
unnecessary change
> down_write(&zram->init_lock);
> if (init_done(zram)) {
> up_write(&zram->init_lock);
> @@ -239,6 +242,7 @@ static struct zram_meta *zram_meta_alloc(u64 disksize)
> {
> size_t num_pages;
> struct zram_meta *meta = kmalloc(sizeof(*meta), GFP_KERNEL);
> +
Ditto
> if (!meta)
> goto out;
>
> @@ -374,6 +378,7 @@ 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;
> +
Ditto
> page = bvec->bv_page;
>
> read_lock(&meta->tb_lock);
> @@ -607,6 +612,7 @@ 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;
> +
Ditto
> if (!handle)
> continue;
>
> @@ -667,6 +673,7 @@ static ssize_t disksize_store(struct device *dev,
> zram->disksize = disksize;
> set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
> revalidate_disk(zram->disk);
> + zram_add_dev();
Why do you add new device unconditionally?
Maybe we need new konb on sysfs or ioctl for adding new device?
Any thought, guys?
> up_write(&zram->init_lock);
> return len;
>
> @@ -954,6 +961,34 @@ static void destroy_device(struct zram *zram)
> blk_cleanup_queue(zram->queue);
> }
>
> +/*
> + * Automatically add empty zram device,
> + * if all created devices already initialized
> + */
> +static inline int zram_add_dev(void)
> +{
> + int dev_id;
> +
> + for (dev_id = 0; dev_id < num_devices; dev_id++) {
> + if (!zram_devices[dev_id].disksize)
> + return 0;
> + }
> +
> + if (max_num_devices <= num_devices) {
> + pr_warn("Can't add zram%u, max device number reached\n", num_devices);
> + return 1;
> + }
> +
> + if (create_device(&zram_devices[num_devices], num_devices)) {
> + destroy_device(&zram_devices[num_devices]);
> + return 1;
> + }
> + pr_info("Created zram%u device\n", num_devices);
> + num_devices++;
Who protects num_devices race?
> +
> + return 0;
> +}
There is only adding function. Where is removing function?
Sorry, I am on vacation tomorrow so pz, understand my late response.
> +
> static int __init zram_init(void)
> {
> int ret, dev_id;
> @@ -972,13 +1007,14 @@ 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)
> @@ -1025,7 +1061,7 @@ 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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--
Kind regards,
Minchan Kim
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