Re: [PATCH 4/5] mm: zswap: add basic meminfo and vmstat coverage

[Johannes Weiner]

On Wed, Apr 27, 2022 at 01:29:34PM -0700, Minchan Kim wrote:
> Hi Johannes,
> 
> On Wed, Apr 27, 2022 at 12:00:15PM -0400, Johannes Weiner wrote:
> > Currently it requires poking at debugfs to figure out the size and
> > population of the zswap cache on a host. There are no counters for
> > reads and writes against the cache. As a result, it's difficult to
> > understand zswap behavior on production systems.
> > 
> > Print zswap memory consumption and how many pages are zswapped out in
> > /proc/meminfo. Count zswapouts and zswapins in /proc/vmstat.
> > 
> > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> > ---
> >  fs/proc/meminfo.c             |  7 +++++++
> >  include/linux/swap.h          |  5 +++++
> >  include/linux/vm_event_item.h |  4 ++++
> >  mm/vmstat.c                   |  4 ++++
> >  mm/zswap.c                    | 13 ++++++-------
> >  5 files changed, 26 insertions(+), 7 deletions(-)
> > 
> > diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
> > index 6fa761c9cc78..6e89f0e2fd20 100644
> > --- a/fs/proc/meminfo.c
> > +++ b/fs/proc/meminfo.c
> > @@ -86,6 +86,13 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
> >  
> >  	show_val_kb(m, "SwapTotal:      ", i.totalswap);
> >  	show_val_kb(m, "SwapFree:       ", i.freeswap);
> > +#ifdef CONFIG_ZSWAP
> > +	seq_printf(m,  "Zswap:          %8lu kB\n",
> > +		   (unsigned long)(zswap_pool_total_size >> 10));
> > +	seq_printf(m,  "Zswapped:       %8lu kB\n",
> > +		   (unsigned long)atomic_read(&zswap_stored_pages) <<
> > +		   (PAGE_SHIFT - 10));
> > +#endif
> 
> I agree it would be very handy to have the memory consumption in meminfo
> 
> https://lore.kernel.org/all/YYwZXrL3Fu8%2FvLZw@xxxxxxxxxx/
> 
> If we really go this Zswap only metric instead of general term
> "Compressed", I'd like to post maybe "Zram:" with same reason
> in this patchset. Do you think that's better idea instead of
> introducing general term like "Compressed:" or something else?

I'm fine with changing it to Compressed. If somebody cares about a
more detailed breakdown, we can add Zswap, Zram subsets as needed.