linux-kernel - Re: [PATCH] mm: show_mem: show number of zspages in show_free

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Message-Id: <20250902031359.170361-1-sj@kernel.org>
Date: Mon,  1 Sep 2025 20:13:59 -0700
From: SeongJae Park <sj@...nel.org>
To: SeongJae Park <sj@...nel.org>
Cc: Thadeu Lima de Souza Cascardo <cascardo@...lia.com>,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Brendan Jackman <jackmanb@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Zi Yan <ziy@...dia.com>,
	kernel-dev@...lia.com
Subject: Re: [PATCH] mm: show_mem: show number of zspages in show_free_areas

On Mon,  1 Sep 2025 18:49:33 -0700 SeongJae Park <sj@...nel.org> wrote:

> Hello,
> 
> On Mon,  1 Sep 2025 15:37:28 -0300 Thadeu Lima de Souza Cascardo <cascardo@...lia.com> wrote:
> 
> > When OOM is triggered, it will show where the pages might be for each zone.
> > When using zram, it might look like lots of pages are missing. After this
> > patch, zspages are shown as below.
> [...]
> > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...lia.com>
> > ---
> >  mm/show_mem.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/mm/show_mem.c b/mm/show_mem.c
> > index 41999e94a56d..ecf20a93ea54 100644
> > --- a/mm/show_mem.c
> > +++ b/mm/show_mem.c
> > @@ -310,6 +310,7 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
> >  			" inactive_file:%lukB"
> >  			" unevictable:%lukB"
> >  			" writepending:%lukB"
> > +			" zspages:%lukB"
> >  			" present:%lukB"
> >  			" managed:%lukB"
> >  			" mlocked:%lukB"
> > @@ -332,6 +333,7 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
> >  			K(zone_page_state(zone, NR_ZONE_INACTIVE_FILE)),
> >  			K(zone_page_state(zone, NR_ZONE_UNEVICTABLE)),
> >  			K(zone_page_state(zone, NR_ZONE_WRITE_PENDING)),
> > +			K(zone_page_state(zone, NR_ZSPAGES)),
> 
> I found latest mm-new fails kunit's um build as below, and 'git bisect' points
> this patch.
> 
>     $ make all compile_commands.json scripts_gdb ARCH=um O=.kunit --jobs=40
>     ERROR:root:In file included from ../mm/show_mem.c:18:
>     ../mm/show_mem.c: In function ‘show_free_areas’:
>     ../mm/show_mem.c:336:49: error: ‘NR_ZSPAGES’ undeclared (first use in this function); did you mean ‘NR_STATS’?
>       336 |                         K(zone_page_state(zone, NR_ZSPAGES)),
>           |                                                 ^~~~~~~~~~
>     [...]
> 
> Maybe some CONFIG_ZSMALLOC undeclard case handling, like below, is needed?
> 
>     --- a/mm/show_mem.c
>     +++ b/mm/show_mem.c
>     @@ -333,7 +333,9 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
>                             K(zone_page_state(zone, NR_ZONE_INACTIVE_FILE)),
>                             K(zone_page_state(zone, NR_ZONE_UNEVICTABLE)),
>                             K(zone_page_state(zone, NR_ZONE_WRITE_PENDING)),
>     +#if IS_ENABLED(CONFIG_ZSMALLOC)
>                             K(zone_page_state(zone, NR_ZSPAGES)),
>     +#endif

Of course, the above example will make the output shows wrong values on
'zspages:' and later fields when ZSMALLOC is unset.  Maybe below change on top
of the above diff makes sense?

    --- a/mm/show_mem.c
    +++ b/mm/show_mem.c
    @@ -335,6 +335,8 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
                            K(zone_page_state(zone, NR_ZONE_WRITE_PENDING)),
     #if IS_ENABLED(CONFIG_ZSMALLOC)
                            K(zone_page_state(zone, NR_ZSPAGES)),
    +#else
    +                       0,
     #endif
                            K(zone->present_pages),
                            K(zone_managed_pages(zone)),


Thanks,
SJ

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