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

[Minchan Kim <minchan@kernel.org>]

Hello David,

On Fri, Aug 22, 2014 at 06:55:38AM -0400, David Horner 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.
> 
> 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.

Thanks for suggesting but as I said, it should be fixed in memparse itself,
not caller if it is really problem so I don't want to touch it in this
patchset. It's not critical for adding the feature.

> 
> >
> > 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.

Thanks.

> 
> > +               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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-- 
Kind regards,
Minchan Kim