[PATCH v2] mm: memcontrol: add {pgscan,pgsteal}_{kswapd,direct} items in memory.stat of cgroup v2

[PATCH v2] mm: memcontrol: add {pgscan,pgsteal}_{kswapd,direct} items in memory.stat of cgroup v2

[Qi Zheng]

There are already statistics of {pgscan,pgsteal}_kswapd and
{pgscan,pgsteal}_direct of memcg event here, but now only the
sum of the two is displayed in memory.stat of cgroup v2.

In order to obtain more accurate information during monitoring
and debugging, and to align with the display in /proc/vmstat,
it better to display {pgscan,pgsteal}_kswapd and
{pgscan,pgsteal}_direct separately.

Also, for forward compatibility, we still display pgscan and
pgsteal items so that it won't break existing applications.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Muchun Song <songmuchun@bytedance.com>
---
Changelog in v1 -> v2:
 - keep pgscan and pgsteal items for forward compatibility, thanks to Shakeel
 - update commit log
 - collect Acked-bys

 Documentation/admin-guide/cgroup-v2.rst | 12 ++++++
 mm/memcontrol.c                         | 54 ++++++++++++-------------
 2 files changed, 38 insertions(+), 28 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 176298f2f4de..b2b55e7360d8 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1445,9 +1445,21 @@ PAGE_SIZE multiple when read back.
 	  pgscan (npn)
 		Amount of scanned pages (in an inactive LRU list)
 
+	  pgscan_kswapd (npn)
+		Amount of scanned pages by kswapd (in an inactive LRU list)
+
+	  pgscan_direct (npn)
+		Amount of scanned pages directly  (in an inactive LRU list)
+
 	  pgsteal (npn)
 		Amount of reclaimed pages
 
+	  pgsteal_kswapd (npn)
+		Amount of reclaimed pages by kswapd
+
+	  pgsteal_direct (npn)
+		Amount of reclaimed pages directly
+
 	  pgactivate (npn)
 		Amount of pages moved to the active LRU list
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0d3fe0a0c75a..fd78c4d6bbc7 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1460,6 +1460,28 @@ static inline unsigned long memcg_page_state_output(struct mem_cgroup *memcg,
 	return memcg_page_state(memcg, item) * memcg_page_state_unit(item);
 }
 
+static const unsigned int memcg_vm_event_stat[] = {
+	PGSCAN_KSWAPD,
+	PGSCAN_DIRECT,
+	PGSTEAL_KSWAPD,
+	PGSTEAL_DIRECT,
+	PGFAULT,
+	PGMAJFAULT,
+	PGREFILL,
+	PGACTIVATE,
+	PGDEACTIVATE,
+	PGLAZYFREE,
+	PGLAZYFREED,
+#if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
+	ZSWPIN,
+	ZSWPOUT,
+#endif
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	THP_FAULT_ALLOC,
+	THP_COLLAPSE_ALLOC,
+#endif
+};
+
 static char *memory_stat_format(struct mem_cgroup *memcg)
 {
 	struct seq_buf s;
@@ -1495,41 +1517,17 @@ static char *memory_stat_format(struct mem_cgroup *memcg)
 	}
 
 	/* Accumulated memory events */
-
-	seq_buf_printf(&s, "%s %lu\n", vm_event_name(PGFAULT),
-		       memcg_events(memcg, PGFAULT));
-	seq_buf_printf(&s, "%s %lu\n", vm_event_name(PGMAJFAULT),
-		       memcg_events(memcg, PGMAJFAULT));
-	seq_buf_printf(&s, "%s %lu\n",  vm_event_name(PGREFILL),
-		       memcg_events(memcg, PGREFILL));
 	seq_buf_printf(&s, "pgscan %lu\n",
 		       memcg_events(memcg, PGSCAN_KSWAPD) +
 		       memcg_events(memcg, PGSCAN_DIRECT));
 	seq_buf_printf(&s, "pgsteal %lu\n",
 		       memcg_events(memcg, PGSTEAL_KSWAPD) +
 		       memcg_events(memcg, PGSTEAL_DIRECT));
-	seq_buf_printf(&s, "%s %lu\n", vm_event_name(PGACTIVATE),
-		       memcg_events(memcg, PGACTIVATE));
-	seq_buf_printf(&s, "%s %lu\n", vm_event_name(PGDEACTIVATE),
-		       memcg_events(memcg, PGDEACTIVATE));
-	seq_buf_printf(&s, "%s %lu\n", vm_event_name(PGLAZYFREE),
-		       memcg_events(memcg, PGLAZYFREE));
-	seq_buf_printf(&s, "%s %lu\n", vm_event_name(PGLAZYFREED),
-		       memcg_events(memcg, PGLAZYFREED));
-
-#if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
-	seq_buf_printf(&s, "%s %lu\n", vm_event_name(ZSWPIN),
-		       memcg_events(memcg, ZSWPIN));
-	seq_buf_printf(&s, "%s %lu\n", vm_event_name(ZSWPOUT),
-		       memcg_events(memcg, ZSWPOUT));
-#endif
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	seq_buf_printf(&s, "%s %lu\n", vm_event_name(THP_FAULT_ALLOC),
-		       memcg_events(memcg, THP_FAULT_ALLOC));
-	seq_buf_printf(&s, "%s %lu\n", vm_event_name(THP_COLLAPSE_ALLOC),
-		       memcg_events(memcg, THP_COLLAPSE_ALLOC));
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+	for (i = 0; i < ARRAY_SIZE(memcg_vm_event_stat); i++)
+		seq_buf_printf(&s, "%s %lu\n",
+			       vm_event_name(memcg_vm_event_stat[i]),
+			       memcg_events(memcg, memcg_vm_event_stat[i]));
 
 	/* The above should easily fit into one page */
 	WARN_ON_ONCE(seq_buf_has_overflowed(&s));
-- 
2.20.1

Re: [PATCH v2] mm: memcontrol: add {pgscan,pgsteal}_{kswapd,direct} items in memory.stat of cgroup v2

[Shakeel Butt]

On Sat, Jun 04, 2022 at 04:22:09PM +0800, Qi Zheng wrote:
> There are already statistics of {pgscan,pgsteal}_kswapd and
> {pgscan,pgsteal}_direct of memcg event here, but now only the
> sum of the two is displayed in memory.stat of cgroup v2.
> 
> In order to obtain more accurate information during monitoring
> and debugging, and to align with the display in /proc/vmstat,
> it better to display {pgscan,pgsteal}_kswapd and
> {pgscan,pgsteal}_direct separately.
> 
> Also, for forward compatibility, we still display pgscan and
> pgsteal items so that it won't break existing applications.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
> Acked-by: Muchun Song <songmuchun@bytedance.com>

Acked-by: Shakeel Butt <shakeelb@google.com>

Re: [PATCH v2] mm: memcontrol: add {pgscan,pgsteal}_{kswapd,direct} items in memory.stat of cgroup v2

[Michal Hocko]

On Sat 04-06-22 16:22:09, Qi Zheng wrote:
> There are already statistics of {pgscan,pgsteal}_kswapd and
> {pgscan,pgsteal}_direct of memcg event here, but now only the
> sum of the two is displayed in memory.stat of cgroup v2.
> 
> In order to obtain more accurate information during monitoring
> and debugging, and to align with the display in /proc/vmstat,
> it better to display {pgscan,pgsteal}_kswapd and
> {pgscan,pgsteal}_direct separately.
> 
> Also, for forward compatibility, we still display pgscan and
> pgsteal items so that it won't break existing applications.

I do not remember why we have chosen to report cumulative stats rather
than the direct and kswapd parts. Looking back when Roman has introduced
those (http://lkml.kernel.org/r/1494530183-30808-1-git-send-email-guro@fb.com)
I do not see any discussion around that. So it was likely just not
a priority.

I have just one question. Say we even decide to have a per memcg kswapd
in some form, would we report that into the same counter?

> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
> Acked-by: Muchun Song <songmuchun@bytedance.com>

In any case
Acked-by: Michal Hocko <mhocko@suse.com>

One nit below
[...]
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 0d3fe0a0c75a..fd78c4d6bbc7 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1460,6 +1460,28 @@ static inline unsigned long memcg_page_state_output(struct mem_cgroup *memcg,
>  	return memcg_page_state(memcg, item) * memcg_page_state_unit(item);
>  }
>  

I would just add the following for clarity

/* Subset of vm_event_item to report for memcg event stats */
> +static const unsigned int memcg_vm_event_stat[] = {
> +	PGSCAN_KSWAPD,
> +	PGSCAN_DIRECT,
> +	PGSTEAL_KSWAPD,
> +	PGSTEAL_DIRECT,
> +	PGFAULT,
> +	PGMAJFAULT,
> +	PGREFILL,
> +	PGACTIVATE,
> +	PGDEACTIVATE,
> +	PGLAZYFREE,
> +	PGLAZYFREED,
> +#if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
> +	ZSWPIN,
> +	ZSWPOUT,
> +#endif
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +	THP_FAULT_ALLOC,
> +	THP_COLLAPSE_ALLOC,
> +#endif
> +};

-- 
Michal Hocko
SUSE Labs

Re: [PATCH v2] mm: memcontrol: add {pgscan,pgsteal}_{kswapd,direct} items in memory.stat of cgroup v2

[Qi Zheng]

On 2022/6/6 8:03 PM, Michal Hocko wrote:
> On Sat 04-06-22 16:22:09, Qi Zheng wrote:
>> There are already statistics of {pgscan,pgsteal}_kswapd and
>> {pgscan,pgsteal}_direct of memcg event here, but now only the
>> sum of the two is displayed in memory.stat of cgroup v2.
>>
>> In order to obtain more accurate information during monitoring
>> and debugging, and to align with the display in /proc/vmstat,
>> it better to display {pgscan,pgsteal}_kswapd and
>> {pgscan,pgsteal}_direct separately.
>>
>> Also, for forward compatibility, we still display pgscan and
>> pgsteal items so that it won't break existing applications.
> 
> I do not remember why we have chosen to report cumulative stats rather
> than the direct and kswapd parts. Looking back when Roman has introduced
> those (http://lkml.kernel.org/r/1494530183-30808-1-git-send-email-guro@fb.com)
> I do not see any discussion around that. So it was likely just not
> a priority.
> 
> I have just one question. Say we even decide to have a per memcg kswapd
> in some form, would we report that into the same counter?

IMO, I would like it can be reported into the same counter.

> 
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
>> Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
>> Acked-by: Muchun Song <songmuchun@bytedance.com>
> 
> In any case
> Acked-by: Michal Hocko <mhocko@suse.com>

Thanks.

> 
> One nit below
> [...]
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 0d3fe0a0c75a..fd78c4d6bbc7 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -1460,6 +1460,28 @@ static inline unsigned long memcg_page_state_output(struct mem_cgroup *memcg,
>>   	return memcg_page_state(memcg, item) * memcg_page_state_unit(item);
>>   }
>>   
> 
> I would just add the following for clarity

OK, will do.

> 
> /* Subset of vm_event_item to report for memcg event stats */
>> +static const unsigned int memcg_vm_event_stat[] = {
>> +	PGSCAN_KSWAPD,
>> +	PGSCAN_DIRECT,
>> +	PGSTEAL_KSWAPD,
>> +	PGSTEAL_DIRECT,
>> +	PGFAULT,
>> +	PGMAJFAULT,
>> +	PGREFILL,
>> +	PGACTIVATE,
>> +	PGDEACTIVATE,
>> +	PGLAZYFREE,
>> +	PGLAZYFREED,
>> +#if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
>> +	ZSWPIN,
>> +	ZSWPOUT,
>> +#endif
>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> +	THP_FAULT_ALLOC,
>> +	THP_COLLAPSE_ALLOC,
>> +#endif
>> +};
> 

-- 
Thanks,
Qi