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

[Dan Streetman <ddstreet@ieee.org>]

On Fri, Aug 22, 2014 at 6:55 AM, David Horner <ds2horner@gmail.com> wrote:
> 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.

Yes by "default" I meant the initial value.

>
> 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.

I'm not sure of the specifics of memparse, but if it returns 0 for
non-numeric strings (which i assume it does, since there's no method
for reporting errors) I agree that should return -EINVAL instead of
clearing the mem_limit.

>
>>
>> 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
>>

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