From: Mel Gorman <mgorman@techsingularity.net>
To: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
Vlastimil Babka <vbabka@suse.cz>,
Michal Hocko <mhocko@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Mel Gorman <mgorman@techsingularity.net>
Subject: [RFC PATCH 0/6] Drain remote per-cpu directly v2
Date: Mon, 9 May 2022 14:07:59 +0100 [thread overview]
Message-ID: <20220509130805.20335-1-mgorman@techsingularity.net> (raw)
Changelog since v1
o Fix unsafe RT locking scheme
o Use spin_trylock on UP PREEMPT_RT
This series has the same intent as Nicolas' series "mm/page_alloc: Remote
per-cpu lists drain support" -- avoid interference of a high priority
task due to a workqueue item draining per-cpu page lists. While many
workloads can tolerate a brief interruption, it may be cause a real-time
task runnning on a NOHZ_FULL CPU to miss a deadline and at minimum,
the draining in non-deterministic.
Currently an IRQ-safe local_lock protects the page allocator per-cpu lists.
The local_lock on its own prevents migration and the IRQ disabling protects
from corruption due to an interrupt arriving while a page allocation is
in progress. The locking is inherently unsafe for remote access unless
the CPU is hot-removed.
This series adjusts the locking. A spinlock is added to struct
per_cpu_pages to protect the list contents while local_lock_irq continues
to prevent migration and IRQ reentry. This allows a remote CPU to safely
drain a remote per-cpu list.
This series is a partial series. Follow-on work should allow the
local_irq_save to be converted to a local_irq to avoid IRQs being
disabled/enabled in most cases. Consequently, there are some TODO comments
highlighting the places that would change if local_irq was used. However,
there are enough corner cases that it deserves a series on its own
separated by one kernel release and the priority right now is to avoid
interference of high priority tasks.
Patch 1 is a cosmetic patch to clarify when page->lru is storing buddy pages
and when it is storing per-cpu pages.
Patch 2 shrinks per_cpu_pages to make room for a spin lock. Strictly speaking
this is not necessary but it avoids per_cpu_pages consuming another
cache line.
Patch 3 is a preparation patch to avoid code duplication.
Patch 4 is a simple micro-optimisation that improves code flow necessary for
a later patch to avoid code duplication.
Patch 5 uses a spin_lock to protect the per_cpu_pages contents while still
relying on local_lock to prevent migration, stabilise the pcp
lookup and prevent IRQ reentrancy.
Patch 6 remote drains per-cpu pages directly instead of using a workqueue.
include/linux/mm_types.h | 5 +
include/linux/mmzone.h | 12 +-
mm/page_alloc.c | 342 +++++++++++++++++++++++++--------------
3 files changed, 230 insertions(+), 129 deletions(-)
--
2.34.1
next reply other threads:[~2022-05-09 13:08 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-09 13:07 Mel Gorman [this message]
2022-05-09 13:08 ` [PATCH 1/6] mm/page_alloc: Add page->buddy_list and page->pcp_list Mel Gorman
2022-05-13 8:41 ` Muchun Song
2022-05-26 10:14 ` Mel Gorman
2022-05-09 13:08 ` [PATCH 2/6] mm/page_alloc: Use only one PCP list for THP-sized allocations Mel Gorman
2022-05-09 13:08 ` [PATCH 3/6] mm/page_alloc: Split out buddy removal code from rmqueue into separate helper Mel Gorman
2022-05-09 13:08 ` [PATCH 4/6] mm/page_alloc: Remove unnecessary page == NULL check in rmqueue Mel Gorman
2022-05-09 13:08 ` [PATCH 5/6] mm/page_alloc: Protect PCP lists with a spinlock Mel Gorman
2022-05-22 2:49 ` Hugh Dickins
2022-05-24 12:12 ` Mel Gorman
2022-05-24 12:19 ` Mel Gorman
2022-05-09 13:08 ` [PATCH 6/6] mm/page_alloc: Remotely drain per-cpu lists Mel Gorman
2022-05-09 15:58 ` [RFC PATCH 0/6] Drain remote per-cpu directly v2 Minchan Kim
2022-05-10 9:27 ` Mel Gorman
2022-05-10 18:13 ` Minchan Kim
2022-05-11 12:47 ` Mel Gorman
2022-05-11 17:20 ` Minchan Kim
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