From: Mel Gorman <mgorman@techsingularity.net>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Nicolas Saenz Julienne <nsaenzju@redhat.com>,
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>
Subject: Re: [PATCH 0/6] Drain remote per-cpu directly v3
Date: Mon, 16 May 2022 11:53:11 +0100 [thread overview]
Message-ID: <20220516105311.GL3441@techsingularity.net> (raw)
In-Reply-To: <20220513123805.41e560392d028c271b36847d@linux-foundation.org>
On Fri, May 13, 2022 at 12:38:05PM -0700, Andrew Morton wrote:
> > The sentence can be dropped because it adds little and is potentially
> > confusing. The PCP being safe to access remotely is specific to the
> > context of the CPU being hot-removed and there are other special corner
> > cases like zone_pcp_disable that modifies a per-cpu structure remotely
> > but not in a way that causes corruption.
>
> OK. I pasted in your para from the other email. Current 0/n blurb:
>
> Some setups, notably NOHZ_FULL CPUs, may be running realtime or
> latency-sensitive applications that cannot tolerate interference due to
> per-cpu drain work queued by __drain_all_pages(). Introduce a new
> mechanism to remotely drain the per-cpu lists. It is made possible by
> remotely locking 'struct per_cpu_pages' new per-cpu spinlocks. This has
> two advantages, the time to drain is more predictable and other unrelated
> tasks are not interrupted.
>
> 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 cause a real-time task running
> on a NOHZ_FULL CPU to miss a deadline and at minimum, the draining is
> 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.
>
> 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.
>
Looks good, thanks!
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2022-05-16 10:53 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-12 8:50 [PATCH 0/6] Drain remote per-cpu directly v3 Mel Gorman
2022-05-12 8:50 ` [PATCH 1/6] mm/page_alloc: Add page->buddy_list and page->pcp_list Mel Gorman
2022-05-13 11:59 ` Nicolas Saenz Julienne
2022-05-19 9:36 ` Vlastimil Babka
2022-05-12 8:50 ` [PATCH 2/6] mm/page_alloc: Use only one PCP list for THP-sized allocations Mel Gorman
2022-05-19 9:45 ` Vlastimil Babka
2022-05-12 8:50 ` [PATCH 3/6] mm/page_alloc: Split out buddy removal code from rmqueue into separate helper Mel Gorman
2022-05-13 12:01 ` Nicolas Saenz Julienne
2022-05-19 9:52 ` Vlastimil Babka
2022-05-23 16:09 ` Qais Yousef
2022-05-24 11:55 ` Mel Gorman
2022-05-25 11:23 ` Qais Yousef
2022-05-12 8:50 ` [PATCH 4/6] mm/page_alloc: Remove unnecessary page == NULL check in rmqueue Mel Gorman
2022-05-13 12:03 ` Nicolas Saenz Julienne
2022-05-19 10:57 ` Vlastimil Babka
2022-05-19 12:13 ` Mel Gorman
2022-05-19 12:26 ` Vlastimil Babka
2022-05-12 8:50 ` [PATCH 5/6] mm/page_alloc: Protect PCP lists with a spinlock Mel Gorman
2022-05-13 12:22 ` Nicolas Saenz Julienne
2022-05-12 8:50 ` [PATCH 6/6] mm/page_alloc: Remotely drain per-cpu lists Mel Gorman
2022-05-12 19:37 ` Andrew Morton
2022-05-13 15:04 ` Mel Gorman
2022-05-13 15:19 ` Nicolas Saenz Julienne
2022-05-13 18:23 ` Mel Gorman
2022-05-17 12:57 ` Mel Gorman
2022-05-12 19:43 ` [PATCH 0/6] Drain remote per-cpu directly v3 Andrew Morton
2022-05-13 14:23 ` Mel Gorman
2022-05-13 19:38 ` Andrew Morton
2022-05-16 10:53 ` Mel Gorman [this message]
2022-05-13 12:24 ` Nicolas Saenz Julienne
2022-05-17 23:35 ` Qian Cai
2022-05-18 12:51 ` Mel Gorman
2022-05-18 16:27 ` Qian Cai
2022-05-18 17:15 ` Paul E. McKenney
2022-05-19 13:29 ` Qian Cai
2022-05-19 19:15 ` Paul E. McKenney
2022-05-19 21:05 ` Qian Cai
2022-05-19 21:29 ` Paul E. McKenney
2022-05-18 17:26 ` Marcelo Tosatti
2022-05-18 17:44 ` Marcelo Tosatti
2022-05-18 18:01 ` Nicolas Saenz Julienne
2022-05-26 17:19 ` Qian Cai
2022-05-27 8:39 ` Mel Gorman
2022-05-27 12:58 ` Qian Cai
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