Re: [PATCH 3/3] zram: add mem_used_max via sysfs

[David Horner <ds2horner@gmail.com>]

The introduction of a reset can cause the stale zero value to be
retained in the show.
Instead reset to current value.

On Wed, Aug 13, 2014 at 9:12 PM, Minchan Kim <minchan@kernel.org> wrote:
> Normally, zram user can get maximum memory zsmalloc consumed via
> polling mem_used_total with sysfs in userspace.
>
> But it has a critical problem because user can miss peak memory
> usage during update interval of polling. For avoiding that,
> user should poll it frequently with mlocking to avoid delay
> when memory pressure is heavy so it would be handy if the
> kernel supports the function.
>
> This patch adds mem_used_max via sysfs.
>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  Documentation/blockdev/zram.txt |  1 +
>  drivers/block/zram/zram_drv.c   | 35 +++++++++++++++++++++++++++++++++--
>  drivers/block/zram/zram_drv.h   |  2 ++
>  3 files changed, 36 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
> index 9f239ff8c444..3b2247c2d4cf 100644
> --- a/Documentation/blockdev/zram.txt
> +++ b/Documentation/blockdev/zram.txt
> @@ -107,6 +107,7 @@ size of the disk when not in use so a huge zram is wasteful.
>                 orig_data_size
>                 compr_data_size
>                 mem_used_total
> +               mem_used_max
>
>  8) Deactivate:
>         swapoff /dev/zram0
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index b48a3d0e9031..311699f18bd5 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -109,6 +109,30 @@ static ssize_t mem_used_total_show(struct device *dev,
>         return scnprintf(buf, PAGE_SIZE, "%llu\n", val);
>  }
>
> +static ssize_t mem_used_max_reset(struct device *dev,
> +               struct device_attribute *attr, const char *buf, size_t len)

perhaps these are local functions, but wouldn't the zs_ prefix still
be appropriate?
> +{
> +       struct zram *zram = dev_to_zram(dev);
> +
> +       down_write(&zram->init_lock);
> +       zram->max_used_bytes = 0;

           zram->max_used_bytes = zs_get_total_size_bytes(meta->mem_pool);

           (where meta is set up as below  (beyond my skill level at
the moment)).

> +       up_write(&zram->init_lock);
> +       return len;
> +}
> +
> +static ssize_t mem_used_max_show(struct device *dev,
> +               struct device_attribute *attr, char *buf)
> +{
> +       u64 max_used_bytes;
> +       struct zram *zram = dev_to_zram(dev);
> +
> +       down_read(&zram->init_lock);

if these are atomic operations, why the (read and write) locks?

> +       max_used_bytes = zram->max_used_bytes;
> +       up_read(&zram->init_lock);
> +
> +       return scnprintf(buf, PAGE_SIZE, "%llu\n", max_used_bytes);
> +}
> +
>  static ssize_t max_comp_streams_show(struct device *dev,
>                 struct device_attribute *attr, char *buf)
>  {
> @@ -474,6 +498,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>         struct zram_meta *meta = zram->meta;
>         struct zcomp_strm *zstrm;
>         bool locked = false;
> +       u64 total_bytes;
>
>         page = bvec->bv_page;
>         if (is_partial_io(bvec)) {
> @@ -543,8 +568,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>                 goto out;
>         }
>
> -       if (zram->limit_bytes &&
> -               zs_get_total_size_bytes(meta->mem_pool) > zram->limit_bytes) {
> +       total_bytes = zs_get_total_size_bytes(meta->mem_pool);
> +       if (zram->limit_bytes && total_bytes > zram->limit_bytes) {
>                 zs_free(meta->mem_pool, handle);
>                 ret = -ENOMEM;
>                 goto out;
> @@ -578,6 +603,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>         /* Update stats */
>         atomic64_add(clen, &zram->stats.compr_data_size);
>         atomic64_inc(&zram->stats.pages_stored);
> +
> +       zram->max_used_bytes = max(zram->max_used_bytes, total_bytes);
>  out:
>         if (locked)
>                 zcomp_strm_release(zram->comp, zstrm);
> @@ -656,6 +683,7 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
>         down_write(&zram->init_lock);
>
>         zram->limit_bytes = 0;
> +       zram->max_used_bytes = 0;
>
>         if (!init_done(zram)) {
>                 up_write(&zram->init_lock);
> @@ -897,6 +925,8 @@ 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_used_max, S_IRUGO | S_IWUSR, mem_used_max_show,
> +               mem_used_max_reset);
>  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,
> @@ -927,6 +957,7 @@ 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_used_max.attr,
>         &dev_attr_mem_limit.attr,
>         &dev_attr_max_comp_streams.attr,
>         &dev_attr_comp_algorithm.attr,
> diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
> index 086c51782e75..aca09b18fcbd 100644
> --- a/drivers/block/zram/zram_drv.h
> +++ b/drivers/block/zram/zram_drv.h
> @@ -111,6 +111,8 @@ struct zram {
>          */
>         u64 disksize;   /* bytes */
>         u64 limit_bytes;
> +       u64 max_used_bytes;
> +
>         int max_comp_streams;
>         struct zram_stats stats;
>         char compressor[10];
> --
> 2.0.0
>

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