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Message-ID: <20140821000617.GD17372@bbox>
Date: Thu, 21 Aug 2014 09:06:17 +0900
From: Minchan Kim <minchan@...nel.org>
To: David Horner <ds2horner@...il.com>
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 Wed, Aug 20, 2014 at 03:53:18PM +0900, Minchan Kim wrote:
> 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@...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")
> >
>
> I wanted to work with "0", "0K", "0M", "0G" but agree it's meaningless
> at the moment so your version is better.
When I tested your way, it makes trobule for use who wanted "echo 0 >
/sys/block/zram0/mem_used_max" because normally echo adds newline.
Although we can guide them to use "echo -n", it's not a handy for users
as well as not consistent with other knobs.
IMO, we shouldn't force uncomfortable way to user for our uncertain
future expandability. So, I will use kstrtoul.
>
>
> > > + 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
> > >
> >
> > --
> > To unsubscribe, send a message with 'unsubscribe linux-mm' in
> > the body to majordomo@...ck.org. For more info on Linux MM,
> > see: http://www.linux-mm.org/ .
> > Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
>
> --
> Kind regards,
> Minchan Kim
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@...ck.org. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
--
Kind regards,
Minchan Kim
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