Re: [PATCH v3 4/4] zram: report maximum used memory

From: David Horner
Date: Wed Aug 20 2014 - 23:03:13 EST

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On Wed, Aug 20, 2014 at 10:41 PM, Minchan Kim <minchan@xxxxxxxxxx> wrote:
> On Wed, Aug 20, 2014 at 10:20:07PM -0400, David Horner wrote:
>> On Wed, Aug 20, 2014 at 8:27 PM, Minchan Kim <minchan@xxxxxxxxxx> 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@xxxxxxxxxx>
>> > ---
>> > 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@xxxxxxxxxx>
>> > +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@xxxxxxxxxx>
>> > 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:
>
> How many does it make tight?
> If it's not a big, I'd like to stick my version.

It is another atomic (memory barrier) read each time through the loop.

But the expect usual case will be the uncontested case - a drop through.

It would only show up in heavily contested situations -

this is another variation that removes the unnecessary read
but retains the programming structure:and naming:

+static inline void update_used_max(struct zram *zram, const unsigned
long pages)
+{
+ u64 old_max, cur_max;
+
+ old_max = atomic64_read(&zram->stats.max_used_pages);
+ do {
+ cur_max = old_max;
+ if (pages > cur_max)
+ old_max = atomic64_cmpxchg(&zram->stats.max_used_pages,
+ cur_max, pages);
+ } while (old_max != cur_max);
+}
+

>
>>
>> +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:
>
> At the moment, we don't need it but it would be good if we need another
> max in future so I will keep in mind. Thanks for the suggestion!
>
>>
>>
>> +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
>> >
>>
>> --
>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>> the body to majordomo@xxxxxxxxxx For more info on Linux MM,
>> see: http://www.linux-mm.org/ .
>> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
>
> --
> Kind regards,
> Minchan Kim
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Next message: Anton Altaparmakov: "Re: Revert "platform/x86/toshiba-apci.c possible bad if test?""
Previous message: Zhouyi Zhou: "Re: [PATCH 1/1] jump_label: tidy jump_label_ratelimit.h"
In reply to: Minchan Kim: "Re: [PATCH v3 4/4] zram: report maximum used memory"
Next in thread: Minchan Kim: "Re: [PATCH v3 4/4] zram: report maximum used memory"
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