Re: [PATCH v2 2/4] mm: memcontrol: change val type to long in __mod_memcg_{lruvec_}state()

[David Laight <david.laight.linux@gmail.com>]

On Thu, 26 Mar 2026 09:19:29 +0000
"Lorenzo Stoakes (Oracle)" <ljs@kernel.org> wrote:

> On Wed, Mar 25, 2026 at 10:13:23PM +0800, Qi Zheng wrote:
> > From: Qi Zheng <zhengqi.arch@bytedance.com>
> >
> > The __mod_memcg_state() and __mod_memcg_lruvec_state() functions are also
> > used to reparent non-hierarchical stats. In this scenario, the values
> > passed to them are accumulated statistics that might be extremely large
> > and exceed the upper limit of a 32-bit integer.
> >
> > Change the val parameter type from int to long in these functions and
> > their corresponding tracepoints (memcg_rstat_stats) to prevent potential
> > overflow issues.

Won't that are be true on 32bit systems?
Which means the underlying values need to be u64 not long.

	David

> >
> > Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>  
> 
> LGTM, so:
> 
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
> 
> > ---
> >  include/trace/events/memcg.h | 10 +++++-----
> >  mm/memcontrol.c              |  8 ++++----
> >  2 files changed, 9 insertions(+), 9 deletions(-)
> >
> > diff --git a/include/trace/events/memcg.h b/include/trace/events/memcg.h
> > index dfe2f51019b4c..51b62c5931fc2 100644
> > --- a/include/trace/events/memcg.h
> > +++ b/include/trace/events/memcg.h
> > @@ -11,14 +11,14 @@
> >
> >  DECLARE_EVENT_CLASS(memcg_rstat_stats,
> >
> > -	TP_PROTO(struct mem_cgroup *memcg, int item, int val),
> > +	TP_PROTO(struct mem_cgroup *memcg, int item, long val),
> >
> >  	TP_ARGS(memcg, item, val),
> >
> >  	TP_STRUCT__entry(
> >  		__field(u64, id)
> >  		__field(int, item)
> > -		__field(int, val)
> > +		__field(long, val)
> >  	),
> >
> >  	TP_fast_assign(
> > @@ -27,20 +27,20 @@ DECLARE_EVENT_CLASS(memcg_rstat_stats,
> >  		__entry->val = val;
> >  	),
> >
> > -	TP_printk("memcg_id=%llu item=%d val=%d",
> > +	TP_printk("memcg_id=%llu item=%d val=%ld",
> >  		  __entry->id, __entry->item, __entry->val)
> >  );
> >
> >  DEFINE_EVENT(memcg_rstat_stats, mod_memcg_state,
> >
> > -	TP_PROTO(struct mem_cgroup *memcg, int item, int val),
> > +	TP_PROTO(struct mem_cgroup *memcg, int item, long val),
> >
> >  	TP_ARGS(memcg, item, val)
> >  );
> >
> >  DEFINE_EVENT(memcg_rstat_stats, mod_memcg_lruvec_state,
> >
> > -	TP_PROTO(struct mem_cgroup *memcg, int item, int val),
> > +	TP_PROTO(struct mem_cgroup *memcg, int item, long val),
> >
> >  	TP_ARGS(memcg, item, val)
> >  );
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 7fb9cbc10dfbb..4a78550f6174e 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -527,7 +527,7 @@ unsigned long lruvec_page_state_local(struct lruvec *lruvec,
> >
> >  #ifdef CONFIG_MEMCG_V1
> >  static void __mod_memcg_lruvec_state(struct mem_cgroup_per_node *pn,
> > -				     enum node_stat_item idx, int val);
> > +				     enum node_stat_item idx, long val);
> >
> >  void reparent_memcg_lruvec_state_local(struct mem_cgroup *memcg,
> >  				       struct mem_cgroup *parent, int idx)
> > @@ -784,7 +784,7 @@ static int memcg_page_state_unit(int item);
> >   * Normalize the value passed into memcg_rstat_updated() to be in pages. Round
> >   * up non-zero sub-page updates to 1 page as zero page updates are ignored.
> >   */
> > -static int memcg_state_val_in_pages(int idx, int val)
> > +static long memcg_state_val_in_pages(int idx, long val)
> >  {
> >  	int unit = memcg_page_state_unit(idx);
> >
> > @@ -831,7 +831,7 @@ static inline void get_non_dying_memcg_end(void)
> >  #endif
> >
> >  static void __mod_memcg_state(struct mem_cgroup *memcg,
> > -			      enum memcg_stat_item idx, int val)
> > +			      enum memcg_stat_item idx, long val)
> >  {
> >  	int i = memcg_stats_index(idx);
> >  	int cpu;
> > @@ -896,7 +896,7 @@ void reparent_memcg_state_local(struct mem_cgroup *memcg,
> >  #endif
> >
> >  static void __mod_memcg_lruvec_state(struct mem_cgroup_per_node *pn,
> > -				     enum node_stat_item idx, int val)
> > +				     enum node_stat_item idx, long val)
> >  {
> >  	struct mem_cgroup *memcg = pn->memcg;
> >  	int i = memcg_stats_index(idx);
> > --
> > 2.20.1
> >  
>