Re: [PATCH 2/3] mm: page_counter: rearrange struct page_counter fields

[Shakeel Butt <shakeelb@google.com>]

On Sun, Aug 21, 2022 at 7:12 PM Feng Tang <feng.tang@intel.com> wrote:
>
> On Mon, Aug 22, 2022 at 08:17:36AM +0800, Shakeel Butt wrote:
> > With memcg v2 enabled, memcg->memory.usage is a very hot member for
> > the workloads doing memcg charging on multiple CPUs concurrently.
> > Particularly the network intensive workloads. In addition, there is a
> > false cache sharing between memory.usage and memory.high on the charge
> > path. This patch moves the usage into a separate cacheline and move all
> > the read most fields into separate cacheline.
> >
> > To evaluate the impact of this optimization, on a 72 CPUs machine, we
> > ran the following workload in a three level of cgroup hierarchy with top
> > level having min and low setup appropriately. More specifically
> > memory.min equal to size of netperf binary and memory.low double of
> > that.
> >
> >  $ netserver -6
> >  # 36 instances of netperf with following params
> >  $ netperf -6 -H ::1 -l 60 -t TCP_SENDFILE -- -m 10K
> >
> > Results (average throughput of netperf):
> > Without (6.0-rc1)     10482.7 Mbps
> > With patch            12413.7 Mbps (18.4% improvement)
> >
> > With the patch, the throughput improved by 18.4%.
> >
> > One side-effect of this patch is the increase in the size of struct
> > mem_cgroup. However for the performance improvement, this additional
> > size is worth it. In addition there are opportunities to reduce the size
> > of struct mem_cgroup like deprecation of kmem and tcpmem page counters
> > and better packing.
> >
> > Signed-off-by: Shakeel Butt <shakeelb@google.com>
> > Reported-by: kernel test robot <oliver.sang@intel.com>
>
> Looks good to me, with one nit below.
>
> Reviewed-by: Feng Tang <feng.tang@intel.com>

Thanks.

>
> > ---
> >  include/linux/page_counter.h | 34 +++++++++++++++++++++++-----------
> >  1 file changed, 23 insertions(+), 11 deletions(-)
> >
> > diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h
> > index 679591301994..8ce99bde645f 100644
> > --- a/include/linux/page_counter.h
> > +++ b/include/linux/page_counter.h
> > @@ -3,15 +3,27 @@
> >  #define _LINUX_PAGE_COUNTER_H
> >
> >  #include <linux/atomic.h>
> > +#include <linux/cache.h>
> >  #include <linux/kernel.h>
> >  #include <asm/page.h>
> >
> > +#if defined(CONFIG_SMP)
> > +struct pc_padding {
> > +     char x[0];
> > +} ____cacheline_internodealigned_in_smp;
> > +#define PC_PADDING(name)     struct pc_padding name
> > +#else
> > +#define PC_PADDING(name)
> > +#endif
>
> There are 2 similar padding definitions in mmzone.h and memcontrol.h:
>
>         struct memcg_padding {
>                 char x[0];
>         } ____cacheline_internodealigned_in_smp;
>         #define MEMCG_PADDING(name)      struct memcg_padding name
>
>         struct zone_padding {
>                 char x[0];
>         } ____cacheline_internodealigned_in_smp;
>         #define ZONE_PADDING(name)      struct zone_padding name;
>
> Maybe we can generalize them, and lift it into include/cache.h? so
> that more places can reuse it in future.
>

This makes sense but let me do that in a separate patch.