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Message-ID: <CAFdhcLQcgME18U2NfEc6dXfvHnJWpyqcMR=Y16MyyghWiNRo1w@mail.gmail.com>
Date: Wed, 20 Aug 2014 02:26:50 -0400
From: David Horner <ds2horner@...il.com>
To: Minchan Kim <minchan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Linux-MM <linux-mm@...ck.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Jerome Marchand <jmarchan@...hat.com>, juno.choi@....com,
seungho1.park@....com, Luigi Semenzato <semenzato@...gle.com>,
Nitin Gupta <ngupta@...are.org>,
Seth Jennings <sjennings@...iantweb.net>,
Dan Streetman <ddstreet@...e.org>
Subject: Re: [PATCH v2 4/4] zram: report maximum used memory
On Tue, Aug 19, 2014 at 3:54 AM, Minchan Kim <minchan@...nel.org> wrote:
> Normally, zram user could get maximum memory usage zram 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 inverval of polling. For avoiding that,
> user should poll it with shorter interval(ie, 0.0000000001s)
> with mlocking to avoid page fault delay when memory pressure
> is heavy. It would be troublesome.
>
> This patch adds new knob "mem_used_max" so user could see
> the maximum memory usage easily via reading the knob and reset
> it via "echo 0 > /sys/block/zram0/mem_used_max".
>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
> Documentation/ABI/testing/sysfs-block-zram | 10 +++++
> Documentation/blockdev/zram.txt | 1 +
> drivers/block/zram/zram_drv.c | 60 +++++++++++++++++++++++++++++-
> drivers/block/zram/zram_drv.h | 1 +
> 4 files changed, 70 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram
> index 025331c19045..ffd1ea7443dd 100644
> --- a/Documentation/ABI/testing/sysfs-block-zram
> +++ b/Documentation/ABI/testing/sysfs-block-zram
> @@ -120,6 +120,16 @@ Description:
> statistic.
> Unit: bytes
>
> +What: /sys/block/zram<id>/mem_used_max
> +Date: August 2014
> +Contact: Minchan Kim <minchan@...nel.org>
> +Description:
> + The mem_used_max file is read/write and specifies the amount
> + of maximum memory zram have consumed to store compressed data.
> + For resetting the value, you should do "echo 0". Otherwise,
> + you could see -EINVAL.
> + Unit: bytes
> +
> What: /sys/block/zram<id>/mem_limit
> Date: August 2014
> Contact: Minchan Kim <minchan@...nel.org>
> 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 adc91c7ecaef..e4d44842a91d 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -149,6 +149,40 @@ static ssize_t mem_limit_store(struct device *dev,
> return len;
> }
>
> +static ssize_t mem_used_max_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + u64 val = 0;
> + struct zram *zram = dev_to_zram(dev);
> +
> + down_read(&zram->init_lock);
> + if (init_done(zram))
> + val = atomic64_read(&zram->stats.max_used_pages);
> + up_read(&zram->init_lock);
> +
> + return scnprintf(buf, PAGE_SIZE, "%llu\n", val << PAGE_SHIFT);
> +}
> +
> +static ssize_t mem_used_max_store(struct device *dev,
> + struct device_attribute *attr, const char *buf, size_t len)
> +{
> + u64 limit;
> + struct zram *zram = dev_to_zram(dev);
> + struct zram_meta *meta = zram->meta;
> +
> - limit = memparse(buf, NULL);
> - if (0 != limit)
we wanted explicit "0" and nothing else for extensibility
if (len != 1 || *buf != "0")
> + return -EINVAL;
> +
> + down_read(&zram->init_lock);
> + if (init_done(zram))
> + atomic64_set(&zram->stats.max_used_pages,
> + zs_get_total_size(meta->mem_pool));
> + up_read(&zram->init_lock);
> +
> + return len;
return 1;
the standard convention is to return used amount of buffer
> +}
> +
> static ssize_t max_comp_streams_store(struct device *dev,
> struct device_attribute *attr, const char *buf, size_t len)
> {
> @@ -461,6 +495,26 @@ out_cleanup:
> return ret;
> }
>
> +static bool check_limit(struct zram *zram)
> +{
> + unsigned long alloced_pages;
> + u64 old_max, cur_max;
> + struct zram_meta *meta = zram->meta;
> +
> + do {
> + alloced_pages = zs_get_total_size(meta->mem_pool);
> + if (zram->limit_pages && alloced_pages > zram->limit_pages)
> + return false;
> +
> + old_max = cur_max = atomic64_read(&zram->stats.max_used_pages);
> + if (alloced_pages > cur_max)
> + old_max = atomic64_cmpxchg(&zram->stats.max_used_pages,
> + cur_max, alloced_pages);
> + } while (old_max != cur_max);
> +
> + return true;
> +}
> +
Check_limit does more than check limit - it has a substantial side
effect of updating max used.
Basically if we already allocated the buffer and our alloced_pages is
less than the limit then we are good to go.
It is the race to update that we need to have the cmpxchg.
And maybe a helper function would aid readability - not sure, see next point.
I don't believe there is need for the loop either.
Any other updater will also be including our allocated pages
(and at this point in the code eliminated from roll back)
so if they beat us to it, then no problem, their max is better than ours.
> static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> int offset)
> {
> @@ -541,8 +595,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> goto out;
> }
>
> - if (zram->limit_pages &&
> - zs_get_total_size(meta->mem_pool) > zram->limit_pages) {
> + if (!check_limit(zram)) {
> zs_free(meta->mem_pool, handle);
> ret = -ENOMEM;
> goto out;
> @@ -897,6 +950,8 @@ 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(mem_used_max, S_IRUGO | S_IWUSR, mem_used_max_show,
> + mem_used_max_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,
> @@ -926,6 +981,7 @@ static struct attribute *zram_disk_attrs[] = {
> &dev_attr_compr_data_size.attr,
> &dev_attr_mem_used_total.attr,
> &dev_attr_mem_limit.attr,
> + &dev_attr_mem_used_max.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 b7aa9c21553f..29383312d543 100644
> --- a/drivers/block/zram/zram_drv.h
> +++ b/drivers/block/zram/zram_drv.h
> @@ -90,6 +90,7 @@ struct zram_stats {
> atomic64_t notify_free; /* no. of swap slot free notifications */
> atomic64_t zero_pages; /* no. of zero filled pages */
> atomic64_t pages_stored; /* no. of pages currently stored */
> + atomic64_t max_used_pages; /* no. of maximum pages stored */
> };
>
> struct zram_meta {
> --
> 2.0.0
>
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