linux-kernel - [PATCH v2 0/3] memcg: optimize charge codepath

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Date:   Thu, 25 Aug 2022 00:05:03 +0000
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <songmuchun@...edance.com>
Cc:     "Michal Koutný" <mkoutny@...e.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Feng Tang <feng.tang@...el.com>,
        Oliver Sang <oliver.sang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>, lkp@...ts.01.org,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Shakeel Butt <shakeelb@...gle.com>
Subject: [PATCH v2 0/3] memcg: optimize charge codepath

Recently Linux networking stack has moved from a very old per socket
pre-charge caching to per-cpu caching to avoid pre-charge fragmentation
and unwarranted OOMs. One impact of this change is that for network
traffic workloads, memcg charging codepath can become a bottleneck. The
kernel test robot has also reported this regression[1]. This patch
series tries to improve the memcg charging for such workloads.

This patch series implement three optimizations:
(A) Reduce atomic ops in page counter update path.
(B) Change layout of struct page_counter to eliminate false sharing
    between usage and high.
(C) Increase the memcg charge batch to 64.

To evaluate the impact of these optimizations, on a 72 CPUs machine, we
ran the following workload in root memcg and then compared with scenario
where the workload is run in a three level of cgroup hierarchy with top
level having min and low setup appropriately.

 $ 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):
1. root memcg		21694.8 Mbps
2. 6.0-rc1		10482.7 Mbps (-51.6%)
3. 6.0-rc1 + (A)	14542.5 Mbps (-32.9%)
4. 6.0-rc1 + (B)	12413.7 Mbps (-42.7%)
5. 6.0-rc1 + (C)	17063.7 Mbps (-21.3%)
6. 6.0-rc1 + (A+B+C)	20120.3 Mbps (-7.2%)

With all three optimizations, the memcg overhead of this workload has
been reduced from 51.6% to just 7.2%.

[1] https://lore.kernel.org/linux-mm/20220619150456.GB34471@xsang-OptiPlex-9020/

Changes since v1:
- Commit message updates
- Instead of explicit padding add align compiler option with struct

Shakeel Butt (3):
  mm: page_counter: remove unneeded atomic ops for low/min
  mm: page_counter: rearrange struct page_counter fields
  memcg: increase MEMCG_CHARGE_BATCH to 64

 include/linux/memcontrol.h   |  7 ++++---
 include/linux/page_counter.h | 34 +++++++++++++++++++++++-----------
 mm/page_counter.c            | 13 ++++++-------
 3 files changed, 33 insertions(+), 21 deletions(-)

-- 
2.37.1.595.g718a3a8f04-goog