linux-kernel - Re: [PATCH 0/6] Drain remote per-cpu directly v3

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Date:   Wed, 18 May 2022 14:26:08 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     Qian Cai <quic_qiancai@...cinc.com>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nicolas Saenz Julienne <nsaenzju@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 0/6] Drain remote per-cpu directly v3

On Tue, May 17, 2022 at 07:35:07PM -0400, Qian Cai wrote:
> On Thu, May 12, 2022 at 09:50:37AM +0100, Mel Gorman wrote:
> > Changelog since v2
> > o More conversions from page->lru to page->[pcp_list|buddy_list]
> > o Additional test results in changelogs
> > 
> > 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.
> 
> Reverting the whole series fixed an issue that offlining a memory
> section blocking for hours on today's linux-next tree.
> 
>  __wait_rcu_gp
>  synchronize_rcu at kernel/rcu/tree.c:3915
>  lru_cache_disable at mm/swap.c:886
>  __alloc_contig_migrate_range at mm/page_alloc.c:9078
>  isolate_single_pageblock at mm/page_isolation.c:405
>  start_isolate_page_range
>  offline_pages
>  memory_subsys_offline
>  device_offline
>  online_store
>  dev_attr_store
>  sysfs_kf_write
>  kernfs_fop_write_iter
>  new_sync_write
>  vfs_write
>  ksys_write
>  __arm64_sys_write
>  invoke_syscall
>  el0_svc_common.constprop.0
>  do_el0_svc
>  el0_svc
>  el0t_64_sync_handler
>  el0t_64_sync
> 
> For full disclosure, I have also reverted the commit 0d523026abd4
> ("mm/page_alloc: fix tracepoint mm_page_alloc_zone_locked()"), so the
> series can be reverted cleanly. But, I can't see how the commit
> 0d523026abd4 could cause this issue at all.

Hi Qian,

The issue is probably due to lack of the following:

https://lore.kernel.org/linux-mm/YmrWK%2FKoU1zrAxPI@fuller.cnet/

Can you please give the patch on the URL a try? 

Thanks!