On Mon, Jun 27, 2022 at 04:07:55PM +0200, Eric Dumazet wrote:

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On Mon, Jun 27, 2022 at 2:34 PM Feng Tang [off-list ref] wrote:

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On Mon, Jun 27, 2022 at 10:46:21AM +0200, Eric Dumazet wrote:

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On Mon, Jun 27, 2022 at 4:38 AM Feng Tang [off-list ref] wrote:

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Thanks Feng. Can you check the value of memory.kmem.tcp.max_usage_in_bytes
in /sys/fs/cgroup/memory/system.slice/lkp-bootstrap.service after making
sure that the netperf test has already run?

memory.kmem.tcp.max_usage_in_bytes:0

Sorry, I made a mistake that in the original report from Oliver, it
was 'cgroup v2' with a 'debian-11.1' rootfs.

When you asked about cgroup info, I tried the job on another tbox, and
the original 'job.yaml' didn't work, so I kept the 'netperf' test
parameters and started a new job which somehow run with a 'debian-10.4'
rootfs and acutally run with cgroup v1.

And as you mentioned cgroup version does make a big difference, that
with v1, the regression is reduced to 1% ~ 5% on different generations
of test platforms. Eric mentioned they also got regression report,
but much smaller one, maybe it's due to the cgroup version?

This was using the current net-next tree.
Used recipe was something like:

Make sure cgroup2 is mounted or mount it by mount -t cgroup2 none $MOUNT_POINT.
Enable memory controller by echo +memory > $MOUNT_POINT/cgroup.subtree_control.
Create a cgroup by mkdir $MOUNT_POINT/job.
Jump into that cgroup by echo $$ > $MOUNT_POINT/job/cgroup.procs.

<Launch tests>

The regression was smaller than 1%, so considered noise compared to
the benefits of the bug fix.

Yes, 1% is just around noise level for a microbenchmark.

I went check the original test data of Oliver's report, the tests was
run 6 rounds and the performance data is pretty stable (0Day's report
will show any std deviation bigger than 2%)

The test platform is a 4 sockets 72C/144T machine, and I run the
same job (nr_tasks = 25% * nr_cpus) on one CascadeLake AP (4 nodes)
and one Icelake 2 sockets platform, and saw 75% and 53% regresson on
them.

In the first email, there is a file named 'reproduce', it shows the
basic test process:

"
  use 'performane' cpufre  governor for all CPUs

  netserver -4 -D
  modprobe sctp
  netperf -4 -H 127.0.0.1 -t SCTP_STREAM_MANY -c -C -l 300 -- -m 10K  &
  netperf -4 -H 127.0.0.1 -t SCTP_STREAM_MANY -c -C -l 300 -- -m 10K  &
  netperf -4 -H 127.0.0.1 -t SCTP_STREAM_MANY -c -C -l 300 -- -m 10K  &
  (repeat 36 times in total)
  ...

"

Which starts 36 (25% of nr_cpus) netperf clients. And the clients number
also matters, I tried to increase the client number from 36 to 72(50%),
and the regression is changed from 69.4% to 73.7%"

This seems like a lot of opportunities for memcg folks :)

struct page_counter has poor field placement [1], and no per-cpu cache.

[1] "atomic_long_t usage" is sharing cache line with read mostly fields.

(struct mem_cgroup also has poor field placement, mainly because of
struct page_counter)

    28.69%  [kernel]       [k] copy_user_enhanced_fast_string
    16.13%  [kernel]       [k] intel_idle_irq
     6.46%  [kernel]       [k] page_counter_try_charge
     6.20%  [kernel]       [k] __sk_mem_reduce_allocated
     5.68%  [kernel]       [k] try_charge_memcg
     5.16%  [kernel]       [k] page_counter_cancel

Yes, I also analyzed the perf-profile data, and made some layout changes
which could recover the changes from 69% to 40%.

7c80b038d23e1f4c 4890b686f4088c90432149bd6de 332b589c49656a45881bca4ecc0
---------------- --------------------------- ---------------------------
     15722           -69.5%       4792           -40.8%       9300        netperf.Throughput_Mbps

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 1bfcfb1af352..aa37bd39116c 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h

@@ -179,14 +179,13 @@ struct cgroup_subsys_state {
        atomic_t online_cnt;

        /* percpu_ref killing and RCU release */
-       struct work_struct destroy_work;
        struct rcu_work destroy_rwork;
-
+       struct cgroup_subsys_state *parent;
+       struct work_struct destroy_work;
        /*
         * PI: the parent css.  Placed here for cache proximity to following
         * fields of the containing structure.
         */
-       struct cgroup_subsys_state *parent;
 };

 /*

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 9ecead1042b9..963b88ab9930 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h

@@ -239,9 +239,6 @@ struct mem_cgroup {
        /* Private memcg ID. Used to ID objects that outlive the cgroup */
        struct mem_cgroup_id id;

-       /* Accounted resources */
-       struct page_counter memory;             /* Both v1 & v2 */
-
        union {
                struct page_counter swap;       /* v2 only */
                struct page_counter memsw;      /* v1 only */

@@ -251,6 +248,9 @@ struct mem_cgroup {
        struct page_counter kmem;               /* v1 only */
        struct page_counter tcpmem;             /* v1 only */

+       /* Accounted resources */
+       struct page_counter memory;             /* Both v1 & v2 */
+
        /* Range enforcement for interrupt charges */
        struct work_struct high_work;

@@ -313,7 +313,6 @@ struct mem_cgroup {
        atomic_long_t           memory_events[MEMCG_NR_MEMORY_EVENTS];
        atomic_long_t           memory_events_local[MEMCG_NR_MEMORY_EVENTS];

-       unsigned long           socket_pressure;

        /* Legacy tcp memory accounting */
        bool                    tcpmem_active;

@@ -349,6 +348,7 @@ struct mem_cgroup {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
        struct deferred_split deferred_split_queue;
 #endif
+       unsigned long           socket_pressure;

        struct mem_cgroup_per_node *nodeinfo[];
 };