Hello, Yi,
On Tue, Sep 01, 2020 at 02:42:47PM +0800, Yi Wang wrote:
> From: zhanglin <zhang.lin16@xxxxxxxxxx>
>
> Add max_num_devices to limit dynamic zram device creation to prevent
> potential OOM
>
> Signed-off-by: zhanglin <zhang.lin16@xxxxxxxxxx>
> ---
> drivers/block/zram/zram_drv.c | 26 +++++++++++++++++++-------
> 1 file changed, 19 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 36d49159140f..4f2c4eef5051 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -43,8 +43,9 @@ static DEFINE_MUTEX(zram_index_mutex);
> static int zram_major;
> static const char *default_compressor = "lzo-rle";
>
> -/* Module params (documentation at end) */
> static unsigned int num_devices = 1;
> +/* Module params (documentation at end) */
> +static unsigned int max_num_devices = 8;
It seems 8 is too small to me by default. How about 256?
Furthemore, I think it would be worth to have in Kconfig.
config ZRAM_DEV_MAX_COUNT
int "Number of zram devices to be created"
depends on ZRAM
default 256
help
blah blah
> /*
> * Pages that compress to sizes equals or greater than this are stored
> * uncompressed in memory.
> @@ -2013,10 +2014,16 @@ static ssize_t hot_add_show(struct class *class,
> struct class_attribute *attr,
> char *buf)
> {
> - int ret;
> + int ret = -ENOSPC;
>
> mutex_lock(&zram_index_mutex);
> + if (num_devices >= max_num_devices) {
> + mutex_unlock(&zram_index_mutex);
> + return ret;
> + }
> ret = zram_add();
> + if (ret >= 0)
> + num_devices += 1;
> mutex_unlock(&zram_index_mutex);
>
> if (ret < 0)
> @@ -2046,8 +2053,10 @@ static ssize_t hot_remove_store(struct class *class,
> zram = idr_find(&zram_index_idr, dev_id);
> if (zram) {
> ret = zram_remove(zram);
> - if (!ret)
> + if (!ret) {
> idr_remove(&zram_index_idr, dev_id);
> + num_devices -= 1;
> + }
> } else {
> ret = -ENODEV;
> }
> @@ -2089,6 +2098,7 @@ static void destroy_devices(void)
> static int __init zram_init(void)
> {
> int ret;
> + unsigned int i;
>
> ret = cpuhp_setup_state_multi(CPUHP_ZCOMP_PREPARE, "block/zram:prepare",
> zcomp_cpu_up_prepare, zcomp_cpu_dead);
> @@ -2111,13 +2121,15 @@ static int __init zram_init(void)
> return -EBUSY;
> }
>
> - while (num_devices != 0) {
> + if (num_devices > max_num_devices)
> + num_devices = max_num_devices;
I am not sure the overriding is a good idea.
Just leave it but just return error if user wanted to pre-create
exceeding max size in configuration.
Thanks.
> +
> + for (i = 0; i < num_devices; i++) {
> mutex_lock(&zram_index_mutex);
> ret = zram_add();
> mutex_unlock(&zram_index_mutex);
> if (ret < 0)
> goto out_error;
> - num_devices--;
> }
>
> return 0;
> @@ -2135,8 +2147,8 @@ static void __exit zram_exit(void)
> module_init(zram_init);
> module_exit(zram_exit);
>
> -module_param(num_devices, uint, 0);
> -MODULE_PARM_DESC(num_devices, "Number of pre-created zram devices");
> +module_param(max_num_devices, uint, 0);
> +MODULE_PARM_DESC(max_num_devices, "Max number of created zram devices");
>
> MODULE_LICENSE("Dual BSD/GPL");
> MODULE_AUTHOR("Nitin Gupta <ngupta@xxxxxxxxxx>");
> --
> 2.17.1
>
