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

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Date:   Wed, 27 Apr 2022 15:16:48 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Johannes Weiner <hannes@...xchg.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 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@...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.

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

> 
> 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
>