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

Johannes Weiner
2022-04-27T21:20:29Z

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.

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