On Wed, Aug 20, 2014 at 02:26:50AM -0400, David Horner wrote:
> On Tue, Aug 19, 2014 at 3:54 AM, 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 | 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@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..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")
>
I wanted to work with "0", "0K", "0M", "0G" but agree it's meaningless
at the moment so your version is better.
> > + 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
If I follow your suggestion, len should be 1 right before returning
so no problem for functionality POV but I agree explicit "1" is better
for readability so your version is better, better.
>
>
>
> > +}
> > +
> > 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.
Hmm, Normally, limit check is best place to update the max although
function name imply just checking the limit and I don't think
code piece for max updating doesn't hurt readbilty.
If you or other reviewer is strong against, I will be happy to
factor out part of max updating into another function because
I think it's just preference problem for small logic and don't want
to waste argue for that.
If you really want it, pz, ping me again.
>
> Basically if we already allocated the buffer and our alloced_pages is
> less than the limit then we are good to go.
Yeb.
>
> 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.
Let's assume we don't have the loop.
CPU A CPU B
alloced_pages = 2001
old_max = cur_max = 2000
alloced_pages = 2005
old_max = cur_max = 2000
cmpxchg(2000, 2000, 2001) -> OK
cmpxchg(2001, 2000, 2005) -> FAIL
So, we lose 2005 which is bigger vaule.
>
>
>
> > 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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--
Kind regards,
Minchan Kim
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