Re: [External] Re: [RESEND PATCH v2 09/12] mm: memcontrol: convert vmstat slab counters to bytes

[Muchun Song]

On Tue, Dec 8, 2020 at 3:46 AM Roman Gushchin <guro@xxxxxx> wrote:
>
> On Sun, Dec 06, 2020 at 06:14:48PM +0800, Muchun Song wrote:
> > the global and per-node counters are stored in pages, however memcg
> > and lruvec counters are stored in bytes. This scheme looks weird.
> > So convert all vmstat slab counters to bytes.
>
> There is a reason for this weird scheme:
> percpu caches (see struct per_cpu_nodestat) are s8, so counting in bytes
> will lead to overfills. Switching to s32 can lead to an increase in
> the cache thrashing, especially on small machines.

Thanks Roman. I see now.

>
> >
> > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> > ---
> >  include/linux/vmstat.h | 17 ++++++++++-------
> >  mm/vmstat.c            | 21 ++++++++++-----------
> >  2 files changed, 20 insertions(+), 18 deletions(-)
> >
> > diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
> > index 322dcbfcc933..fd1a3d5d4926 100644
> > --- a/include/linux/vmstat.h
> > +++ b/include/linux/vmstat.h
> > @@ -197,18 +197,26 @@ static inline
> >  unsigned long global_node_page_state_pages(enum node_stat_item item)
> >  {
> >       long x = atomic_long_read(&vm_node_stat[item]);
> > +
> >  #ifdef CONFIG_SMP
> >       if (x < 0)
> >               x = 0;
> >  #endif
> > +     if (vmstat_item_in_bytes(item))
> > +             x >>= PAGE_SHIFT;
> >       return x;
> >  }
> >
> >  static inline unsigned long global_node_page_state(enum node_stat_item item)
> >  {
> > -     VM_WARN_ON_ONCE(vmstat_item_in_bytes(item));
> > +     long x = atomic_long_read(&vm_node_stat[item]);
> >
> > -     return global_node_page_state_pages(item);
> > +     VM_WARN_ON_ONCE(vmstat_item_in_bytes(item));
> > +#ifdef CONFIG_SMP
> > +     if (x < 0)
> > +             x = 0;
> > +#endif
> > +     return x;
> >  }
> >
> >  static inline unsigned long zone_page_state(struct zone *zone,
> > @@ -312,11 +320,6 @@ static inline void __mod_zone_page_state(struct zone *zone,
> >  static inline void __mod_node_page_state(struct pglist_data *pgdat,
> >                       enum node_stat_item item, int delta)
> >  {
> > -     if (vmstat_item_in_bytes(item)) {
> > -             VM_WARN_ON_ONCE(delta & (PAGE_SIZE - 1));
> > -             delta >>= PAGE_SHIFT;
> > -     }
> > -
> >       node_page_state_add(delta, pgdat, item);
> >  }
> >
> > diff --git a/mm/vmstat.c b/mm/vmstat.c
> > index 8d77ee426e22..7fb0c7cb9516 100644
> > --- a/mm/vmstat.c
> > +++ b/mm/vmstat.c
> > @@ -345,11 +345,6 @@ void __mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item,
> >       long x;
> >       long t;
> >
> > -     if (vmstat_item_in_bytes(item)) {
> > -             VM_WARN_ON_ONCE(delta & (PAGE_SIZE - 1));
> > -             delta >>= PAGE_SHIFT;
> > -     }
> > -
> >       x = delta + __this_cpu_read(*p);
> >
> >       t = __this_cpu_read(pcp->stat_threshold);
> > @@ -554,11 +549,6 @@ static inline void mod_node_state(struct pglist_data *pgdat,
> >       s8 __percpu *p = pcp->vm_node_stat_diff + item;
> >       long o, n, t, z;
> >
> > -     if (vmstat_item_in_bytes(item)) {
> > -             VM_WARN_ON_ONCE(delta & (PAGE_SIZE - 1));
> > -             delta >>= PAGE_SHIFT;
> > -     }
> > -
> >       do {
> >               z = 0;  /* overflow to node counters */
> >
> > @@ -1012,19 +1002,28 @@ unsigned long node_page_state_pages(struct pglist_data *pgdat,
> >                                   enum node_stat_item item)
> >  {
> >       long x = atomic_long_read(&pgdat->vm_stat[item]);
> > +
> >  #ifdef CONFIG_SMP
> >       if (x < 0)
> >               x = 0;
> >  #endif
> > +     if (vmstat_item_in_bytes(item))
> > +             x >>= PAGE_SHIFT;
> >       return x;
> >  }
> >
> >  unsigned long node_page_state(struct pglist_data *pgdat,
> >                             enum node_stat_item item)
> >  {
> > +     long x = atomic_long_read(&pgdat->vm_stat[item]);
> > +
> >       VM_WARN_ON_ONCE(vmstat_item_in_bytes(item));
> >
> > -     return node_page_state_pages(pgdat, item);
> > +#ifdef CONFIG_SMP
> > +     if (x < 0)
> > +             x = 0;
> > +#endif
> > +     return x;
> >  }
> >  #endif
> >
> > --
> > 2.11.0
> >



-- 
Yours,
Muchun