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    Subject[PATCH v2 00/11] 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.

    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 | 3
    kernel/fork.c | 2
    kernel/scs.c | 2
    mm/vmstat.c | 424 ++++++++++++++++++++++++++++++++++++++++++++++++------------------------------------------
    9 files changed, 308 insertions(+), 223 deletions(-)




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