linux-kernel - [PATCH v4 00/12] fold per-CPU vmstats remotely

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Message-ID: <20230305133657.255737580@redhat.com>
Date:   Sun, 05 Mar 2023 10:36:57 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     Christoph Lameter <cl@...ux.com>
Cc:     Aaron Tomlin <atomlin@...mlin.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Russell King <linux@...linux.org.uk>,
        Huacai Chen <chenhuacai@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>, x86@...nel.org
Subject: [PATCH v4 00/12] fold per-CPU vmstats remotely

This patch series addresses the following two problems:

    1. A customer provided some evidence which indicates that
       the idle tick was stopped; albeit, CPU-specific vmstat
       counters still remained populated.

       Thus one can only assume quiet_vmstat() was not
       invoked on return to the idle loop. If I understand
       correctly, I suspect this divergence might erroneously
       prevent a reclaim attempt by kswapd. If the number of
       zone specific free pages are below their per-cpu drift
       value then zone_page_state_snapshot() is used to
       compute a more accurate view of the aforementioned
       statistic.  Thus any task blocked on the NUMA node
       specific pfmemalloc_wait queue will be unable to make
       significant progress via direct reclaim unless it is
       killed after being woken up by kswapd
       (see throttle_direct_reclaim())

    2. With a SCHED_FIFO task that busy loops on a given CPU,
       and kworker for that CPU at SCHED_OTHER priority,
       queuing work to sync per-vmstats will either cause that
       work to never execute, or stalld (i.e. stall daemon)
       boosts kworker priority which causes a latency
       violation

By having vmstat_shepherd flush the per-CPU counters to the
global counters from remote CPUs.

This is done using cmpxchg to manipulate the counters,
both CPU locally (via the account functions),
and remotely (via cpu_vm_stats_fold).

Thanks to Aaron Tomlin for diagnosing issue 1 and writing
the initial patch series.

v4:
- Switch per-CPU vmstat counters to s32, required for
  architectures that do not provide cmpxchg/xchg on
  8 bits

v3:
- Removed unused drain_zone_pages and changes variable (David Hildenbrand)
- Use xchg instead of cmpxchg in refresh_cpu_vm_stats  (Peter Xu)
- Add drain_all_pages to vmstat_refresh to make
  stats more accurate				       (Peter Xu)
- Improve changelog of
  "mm/vmstat: switch counter modification to cmpxchg"  (Peter Xu / David)
- Improve changelog of
  "mm/vmstat: remove remote node draining"	       (David Hildenbrand)


v2:
- actually use LOCK CMPXCHG on counter mod/inc/dec functions
  (Christoph Lameter)
- use try_cmpxchg for cmpxchg loops
  (Uros Bizjak / Matthew Wilcox)


 arch/arm64/include/asm/percpu.h     |   16 ++
 arch/loongarch/include/asm/percpu.h |   23 +++
 arch/s390/include/asm/percpu.h      |    5 
 arch/x86/include/asm/percpu.h       |   39 +++---
 include/asm-generic/percpu.h        |   17 ++
 include/linux/mmzone.h              |   11 -
 include/linux/percpu-defs.h         |    2 
 kernel/fork.c                       |    2 
 kernel/scs.c                        |    2 
 mm/page_alloc.c                     |   23 ---
 mm/vmstat.c                         |  452 +++++++++++++++++++++++++++++++++++++++++------------------------------------
 11 files changed, 325 insertions(+), 267 deletions(-)