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Date: Wed, 20 Aug 2014 22:20:07 -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 v3 4/4] zram: report maximum used memory
On Wed, Aug 20, 2014 at 8:27 PM, 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 | 57 ++++++++++++++++++++++++++++--
> drivers/block/zram/zram_drv.h | 1 +
> 4 files changed, 67 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..138787579478 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -149,6 +149,41 @@ 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)
> +{
> + int err;
> + unsigned long val;
> + struct zram *zram = dev_to_zram(dev);
> + struct zram_meta *meta = zram->meta;
> +
> + err = kstrtoul(buf, 10, &val);
> + if (err || val != 0)
> + return -EINVAL;
> +
Yes - this works better for the user than explicit single "0" check
Thanks for testing.
> + 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;
> +}
> +
> static ssize_t max_comp_streams_store(struct device *dev,
> struct device_attribute *attr, const char *buf, size_t len)
> {
> @@ -461,6 +496,18 @@ out_cleanup:
> return ret;
> }
>
> +static inline void update_used_max(struct zram *zram, const unsigned long pages)
> +{
> + u64 old_max, cur_max;
> +
> + do {
> + old_max = cur_max = atomic64_read(&zram->stats.max_used_pages);
> + if (pages > cur_max)
> + old_max = atomic64_cmpxchg(&zram->stats.max_used_pages,
> + cur_max, pages);
> + } while (old_max != cur_max);
> +}
> +
This can be tightened up some:
+static inline void update_used_max(struct zram *zram, const unsigned
long pages)
+{
+ u64 prev_max, old_max = 0;
+
+ prev_max = atomic64_read(&zram->stats.max_used_pages);
+ do while (pages > prev_max && prev_max != old_max) {
+ old_max = prev_max;
+ prev_max = atomic64_cmpxchg(&zram->stats.max_used_pages,
+ old_max, pages);
+ };
+}
+
And then can be generalized to:
+static inline void update_max(uint64_t *addr, const uint64_t newvalue)
+{
+ uint64_t prev_max, old_max = 0;
+
+ prev_max = atomic64_read(addr);
+ do while (pages > prev_max && prev_max != old_max) {
+ old_max = prev_max;
+ prev_max = atomic64_cmpxchg(addr,
+ old_max, newvalue);
+ };
+}
+
Called with : update_max(&zram->stats.max_used_pages, alloced_pages).
(I hope I got all the datatypes (I understand there are some implicit
casts) and modes correct).
The idea should be clear.
> static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> int offset)
> {
> @@ -472,6 +519,7 @@ 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;
> + unsigned long alloced_pages;
>
> page = bvec->bv_page;
> if (is_partial_io(bvec)) {
> @@ -541,13 +589,15 @@ 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) {
> + alloced_pages = zs_get_total_size(meta->mem_pool);
> + if (zram->limit_pages && alloced_pages > zram->limit_pages) {
> zs_free(meta->mem_pool, handle);
> ret = -ENOMEM;
> goto out;
> }
>
> + update_used_max(zram, alloced_pages);
> +
or generalized with update_max
> cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_WO);
>
> if ((clen == PAGE_SIZE) && !is_partial_io(bvec)) {
> @@ -897,6 +947,8 @@ 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 +978,7 @@ 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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