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

    > ---
    > 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.

    Thanks,
    Feng

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