On Mon, Jun 27, 2022 at 8:49 PM Feng Tang [off-list ref] wrote:

On Mon, Jun 27, 2022 at 06:25:59PM +0200, Eric Dumazet wrote:

quoted

On Mon, Jun 27, 2022 at 4:48 PM Feng Tang [off-list ref] wrote:

quoted

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

I simply did the following and got much better results.

But I am not sure if updates to ->usage are really needed that often...

diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h
index 679591301994d316062f92b275efa2459a8349c9..e267be4ba849760117d9fd041e22c2a44658ab36

100644

--- a/include/linux/page_counter.h
+++ b/include/linux/page_counter.h

@@ -3,12 +3,15 @@
 #define _LINUX_PAGE_COUNTER_H

 #include <linux/atomic.h>
+#include <linux/cache.h>
 #include <linux/kernel.h>
 #include <asm/page.h>

 struct page_counter {
-       atomic_long_t usage;
-       unsigned long min;
+       /* contended cache line. */
+       atomic_long_t usage ____cacheline_aligned_in_smp;
+
+       unsigned long min ____cacheline_aligned_in_smp;
        unsigned long low;
        unsigned long high;
        unsigned long max;

@@ -27,12 +30,6 @@ struct page_counter {
        unsigned long watermark;
        unsigned long failcnt;

-       /*
-        * 'parent' is placed here to be far from 'usage' to reduce
-        * cache false sharing, as 'usage' is written mostly while
-        * parent is frequently read for cgroup's hierarchical
-        * counting nature.
-        */
        struct page_counter *parent;
 };

I just tested it, it does perform better (the 4th is with your patch),
some perf-profile data is also listed.

 7c80b038d23e1f4c 4890b686f4088c90432149bd6de 332b589c49656a45881bca4ecc0 e719635902654380b23ffce908d
---------------- --------------------------- --------------------------- ---------------------------
     15722           -69.5%       4792           -40.8%       9300           -27.9%      11341        netperf.Throughput_Mbps

      0.00            +0.3        0.26 ±  5%      +0.5        0.51            +1.3        1.27 ±  2%pp.self.__sk_mem_raise_allocated
      0.00            +0.3        0.32 ± 15%      +1.7        1.74 ±  2%      +0.4        0.40 ±  2%  pp.self.propagate_protected_usage
      0.00            +0.8        0.82 ±  7%      +0.9        0.90            +0.8        0.84        pp.self.__mod_memcg_state
      0.00            +1.2        1.24 ±  4%      +1.0        1.01            +1.4        1.44        pp.self.try_charge_memcg
      0.00            +2.1        2.06            +2.1        2.13            +2.1        2.11        pp.self.page_counter_uncharge
      0.00            +2.1        2.14 ±  4%      +2.7        2.71            +2.6        2.60 ±  2%  pp.self.page_counter_try_charge
      1.12 ±  4%      +3.1        4.24            +1.1        2.22            +1.4        2.51        pp.self.native_queued_spin_lock_slowpath
      0.28 ±  9%      +3.8        4.06 ±  4%      +0.2        0.48            +0.4        0.68        pp.self.sctp_eat_data
      0.00            +8.2        8.23            +0.8        0.83            +1.3        1.26        pp.self.__sk_mem_reduce_allocated

And the size of 'mem_cgroup' is increased from 4224 Bytes to 4608.

Hi Feng, can you please try two more configurations? Take Eric's patch
of adding ____cacheline_aligned_in_smp in page_counter and for first
increase MEMCG_CHARGE_BATCH to 64 and for second increase it to 128.
Basically batch increases combined with Eric's patch.