linux-kernel - [PATCH 0/6 v2] mm: LRU drain flush on nohz

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Message-ID: <20250209223005.11519-1-frederic@kernel.org>
Date: Sun,  9 Feb 2025 23:29:58 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oleg Nesterov <oleg@...hat.com>,
	linux-mm@...ck.org
Subject: [PATCH 0/6 v2] mm: LRU drain flush on nohz_full

When LRUs are pending, the drain can be triggered remotely, whether the
remote CPU is running in userspace in nohz_full mode or not. This kind
of noise is expected to be caused by preparatory work before a task
runs isolated in userspace. This patchset is a proposal to flush that
before the task starts its critical work in userspace.

Changes since v1:

_ Various task_work improvements (Oleg)

_ Remove leftover comment on numa_work (Valentin)

_ Add Reviewed-by tag from Valentin

_ Use housekeeping_cpu() instead of housekeeping_test_cpu() on
  fastpath to benefit from static branch (Vlastimil)

_ Spare the actual remote LRU drain when the target CPU is nohz_full. It
  is assumed the LRU drain will happen locally eventually. (Michal)

Frederic Weisbecker (6):
  task_work: Provide means to check if a work is queued
  sched/fair: Use task_work_queued() on numa_work
  sched: Use task_work_queued() on cid_work
  tick/nohz: Move nohz_full related fields out of hot task struct's
    places
  sched/isolation: Introduce isolated task work
  mm: Drain LRUs upon resume to userspace on nohz_full CPUs

 include/linux/sched.h           | 15 +++++++++------
 include/linux/sched/isolation.h | 17 +++++++++++++++++
 include/linux/swap.h            |  1 +
 include/linux/task_work.h       | 12 ++++++++++++
 kernel/sched/core.c             |  6 ++----
 kernel/sched/fair.c             |  5 +----
 kernel/sched/isolation.c        | 34 +++++++++++++++++++++++++++++++++
 kernel/sched/sched.h            |  1 +
 kernel/task_work.c              | 11 +++++++++--
 mm/swap.c                       |  8 +++++++-
 10 files changed, 93 insertions(+), 17 deletions(-)

-- 
2.46.0