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

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Date:   Wed, 27 Apr 2022 17:20:29 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 4/5] mm: zswap: add basic meminfo and vmstat coverage

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@...xchg.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@google.com/
> 
> 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@...xchg.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@...xchg.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