Re: [PATCH v4 3/4] zram: zram memory size limitation

[David Horner <ds2horner@gmail.com>]

On Thu, Aug 21, 2014 at 8:42 PM, Minchan Kim <minchan@kernel.org> wrote:
> Since zram has no control feature to limit memory usage,
> it makes hard to manage system memrory.
>
> This patch adds new knob "mem_limit" via sysfs to set up the
> a limit so that zram could fail allocation once it reaches
> the limit.
>
> In addition, user could change the limit in runtime so that
> he could manage the memory more dynamically.
>
- Default is no limit so it doesn't break old behavior.
+ Initial state is no limit so it doesn't break old behavior.

I understand your previous post now.

I was saying that setting to either a null value or garbage
 (which is interpreted as zero by memparse(buf, NULL);)
removes the limit.

I think this is "surprise" behaviour and rather the null case should
return  -EINVAL
The test below should be "good enough" though not catching all garbage.

>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  Documentation/ABI/testing/sysfs-block-zram | 10 ++++++++
>  Documentation/blockdev/zram.txt            | 24 ++++++++++++++---
>  drivers/block/zram/zram_drv.c              | 41 ++++++++++++++++++++++++++++++
>  drivers/block/zram/zram_drv.h              |  5 ++++
>  4 files changed, 76 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram
> index 70ec992514d0..b8c779d64968 100644
> --- a/Documentation/ABI/testing/sysfs-block-zram
> +++ b/Documentation/ABI/testing/sysfs-block-zram
> @@ -119,3 +119,13 @@ Description:
>                 efficiency can be calculated using compr_data_size and this
>                 statistic.
>                 Unit: bytes
> +
> +What:          /sys/block/zram<id>/mem_limit
> +Date:          August 2014
> +Contact:       Minchan Kim <minchan@kernel.org>
> +Description:
> +               The mem_limit file is read/write and specifies the amount
> +               of memory to be able to consume memory to store store
> +               compressed data. The limit could be changed in run time
> -               and "0" is default which means disable the limit.
> +               and "0" means disable the limit. No limit is the initial state.

there should be no default in the API.

> +               Unit: bytes
> diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
> index 0595c3f56ccf..82c6a41116db 100644
> --- a/Documentation/blockdev/zram.txt
> +++ b/Documentation/blockdev/zram.txt
> @@ -74,14 +74,30 @@ There is little point creating a zram of greater than twice the size of memory
>  since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the
>  size of the disk when not in use so a huge zram is wasteful.
>
> -5) Activate:
> +5) Set memory limit: Optional
> +       Set memory limit by writing the value to sysfs node 'mem_limit'.
> +       The value can be either in bytes or you can use mem suffixes.
> +       In addition, you could change the value in runtime.
> +       Examples:
> +           # limit /dev/zram0 with 50MB memory
> +           echo $((50*1024*1024)) > /sys/block/zram0/mem_limit
> +
> +           # Using mem suffixes
> +           echo 256K > /sys/block/zram0/mem_limit
> +           echo 512M > /sys/block/zram0/mem_limit
> +           echo 1G > /sys/block/zram0/mem_limit
> +
> +           # To disable memory limit
> +           echo 0 > /sys/block/zram0/mem_limit
> +
> +6) Activate:
>         mkswap /dev/zram0
>         swapon /dev/zram0
>
>         mkfs.ext4 /dev/zram1
>         mount /dev/zram1 /tmp
>
> -6) Stats:
> +7) Stats:
>         Per-device statistics are exported as various nodes under
>         /sys/block/zram<id>/
>                 disksize
> @@ -96,11 +112,11 @@ size of the disk when not in use so a huge zram is wasteful.
>                 compr_data_size
>                 mem_used_total
>
> -7) Deactivate:
> +8) Deactivate:
>         swapoff /dev/zram0
>         umount /dev/zram1
>
> -8) Reset:
> +9) Reset:
>         Write any positive value to 'reset' sysfs node
>         echo 1 > /sys/block/zram0/reset
>         echo 1 > /sys/block/zram1/reset
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index f0b8b30a7128..370c355eb127 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -122,6 +122,33 @@ static ssize_t max_comp_streams_show(struct device *dev,
>         return scnprintf(buf, PAGE_SIZE, "%d\n", val);
>  }
>
> +static ssize_t mem_limit_show(struct device *dev,
> +               struct device_attribute *attr, char *buf)
> +{
> +       u64 val;
> +       struct zram *zram = dev_to_zram(dev);
> +
> +       down_read(&zram->init_lock);
> +       val = zram->limit_pages;
> +       up_read(&zram->init_lock);
> +
> +       return scnprintf(buf, PAGE_SIZE, "%llu\n", val << PAGE_SHIFT);
> +}
> +
> +static ssize_t mem_limit_store(struct device *dev,
> +               struct device_attribute *attr, const char *buf, size_t len)
> +{
> +       u64 limit;
> +       struct zram *zram = dev_to_zram(dev);
> +
> +       limit = memparse(buf, NULL);

            if (limit = 0 && buf != "0")
                  return  -EINVAL

> +       down_write(&zram->init_lock);
> +       zram->limit_pages = PAGE_ALIGN(limit) >> PAGE_SHIFT;
> +       up_write(&zram->init_lock);
> +
> +       return len;
> +}
> +
>  static ssize_t max_comp_streams_store(struct device *dev,
>                 struct device_attribute *attr, const char *buf, size_t len)
>  {
> @@ -513,6 +540,14 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>                 ret = -ENOMEM;
>                 goto out;
>         }
> +
> +       if (zram->limit_pages &&
> +               zs_get_total_pages(meta->mem_pool) > zram->limit_pages) {
> +               zs_free(meta->mem_pool, handle);
> +               ret = -ENOMEM;
> +               goto out;
> +       }
> +
>         cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_WO);
>
>         if ((clen == PAGE_SIZE) && !is_partial_io(bvec)) {
> @@ -617,6 +652,9 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
>         struct zram_meta *meta;
>
>         down_write(&zram->init_lock);
> +
> +       zram->limit_pages = 0;
> +
>         if (!init_done(zram)) {
>                 up_write(&zram->init_lock);
>                 return;
> @@ -857,6 +895,8 @@ static DEVICE_ATTR(initstate, S_IRUGO, initstate_show, NULL);
>  static DEVICE_ATTR(reset, S_IWUSR, NULL, reset_store);
>  static DEVICE_ATTR(orig_data_size, S_IRUGO, orig_data_size_show, NULL);
>  static DEVICE_ATTR(mem_used_total, S_IRUGO, mem_used_total_show, NULL);
> +static DEVICE_ATTR(mem_limit, S_IRUGO | S_IWUSR, mem_limit_show,
> +               mem_limit_store);
>  static DEVICE_ATTR(max_comp_streams, S_IRUGO | S_IWUSR,
>                 max_comp_streams_show, max_comp_streams_store);
>  static DEVICE_ATTR(comp_algorithm, S_IRUGO | S_IWUSR,
> @@ -885,6 +925,7 @@ static struct attribute *zram_disk_attrs[] = {
>         &dev_attr_orig_data_size.attr,
>         &dev_attr_compr_data_size.attr,
>         &dev_attr_mem_used_total.attr,
> +       &dev_attr_mem_limit.attr,
>         &dev_attr_max_comp_streams.attr,
>         &dev_attr_comp_algorithm.attr,
>         NULL,
> diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
> index e0f725c87cc6..b7aa9c21553f 100644
> --- a/drivers/block/zram/zram_drv.h
> +++ b/drivers/block/zram/zram_drv.h
> @@ -112,6 +112,11 @@ struct zram {
>         u64 disksize;   /* bytes */
>         int max_comp_streams;
>         struct zram_stats stats;
> +       /*
> +        * the number of pages zram can consume for storing compressed data
> +        */
> +       unsigned long limit_pages;
> +
>         char compressor[10];
>  };
>  #endif
> --
> 2.0.0
>