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

Minchan Kim
2022-04-27T22:16:48Z

On Wed, Apr 27, 2022 at 05:20:29PM -0400, Johannes Weiner wrote:
> 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-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> > > ---
> > > 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-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org/
> >
> > 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.

Thanks! Please consider ZSWPIN to rename more general term, too.

>
> From 8e9e2d6490b7082c41743fbdb9ffd2db4e3ce962 Mon Sep 17 00:00:00 2001
> From: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> Date: Wed, 27 Apr 2022 17:15:15 -0400
> Subject: [PATCH] mm: zswap: add basic meminfo and vmstat coverage fix fix
>
> Signed-off-by: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
> ---
> Documentation/filesystems/proc.rst | 7 ++++---
> fs/proc/meminfo.c | 2 +-
> 2 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 8b5a94cfa722..93edcf233464 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -964,7 +964,7 @@ Example output. You may not have all of these fields.
> Mlocked: 0 kB
> SwapTotal: 0 kB
> SwapFree: 0 kB
> - Zswap: 1904 kB
> + Compressed: 1904 kB
> Zswapped: 7792 kB
> Dirty: 12 kB
> Writeback: 0 kB
> @@ -1057,8 +1057,9 @@ SwapTotal
> SwapFree
> Memory which has been evicted from RAM, and is temporarily
> on the disk
> -Zswap
> - Memory consumed by the zswap backend (compressed size)
> +Compressed
> + Memory consumed by compression backends, such as zswap
> + (compressed size)
> Zswapped
> Amount of anonymous memory stored in zswap (original size)
> Dirty
> diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
> index 6e89f0e2fd20..554d6f230e67 100644
> --- a/fs/proc/meminfo.c
> +++ b/fs/proc/meminfo.c
> @@ -87,7 +87,7 @@ 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",
> + seq_printf(m, "Compressed: %8lu kB\n",
> (unsigned long)(zswap_pool_total_size >> 10));
> seq_printf(m, "Zswapped: %8lu kB\n",
> (unsigned long)atomic_read(&zswap_stored_pages) <<
> --
> 2.35.3
>