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

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Date:   Wed, 27 Apr 2022 13:29:34 -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

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?