Re: [v5 1/2] mm: disable interrupts while initializing deferred pages

From: Pavel Tatashin <pasha.tatashin@oracle.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: steven.sistare@oracle.com, daniel.m.jordan@oracle.com,
	m.mizuma@jp.fujitsu.com, mhocko@suse.com,
	catalin.marinas@arm.com, takahiro.akashi@linaro.org,
	gi-oh.kim@profitbricks.com, heiko.carstens@de.ibm.com,
	baiyaowei@cmss.chinamobile.com, richard.weiyang@gmail.com,
	paul.burton@mips.com, miles.chen@mediatek.com, vbabka@suse.cz,
	mgorman@suse.de, hannes@cmpxchg.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [v5 1/2] mm: disable interrupts while initializing deferred pages
Date: Tue, 13 Mar 2018 15:45:46 -0400	[thread overview]
Message-ID: <20180313194546.k62tni4g4gnds2nx@xakep.localdomain> (raw)
In-Reply-To: <20180313115549.7badec1c6b85eb5a1cf21eb6@linux-foundation.org>

> > 
> > We must remove cond_resched() because we can't sleep anymore. They were
> > added to fight NMI timeouts, so I will replace them with
> > touch_nmi_watchdog() in a follow-up fix.
> 
> This makes no sense.  Any code section where we can add cond_resched()
> was never subject to NMI timeouts because that code cannot be running with
> disabled interrupts.
> 

Hi Andrew,

I was talking about this patch:

9b6e63cbf85b89b2dbffa4955dbf2df8250e5375
mm, page_alloc: add scheduling point to memmap_init_zone

Which adds cond_resched() to memmap_init_zone() to avoid NMI timeouts.

memmap_init_zone() is used both, early in boot, when non-deferred struct
pages are initialized, but also may be used later, during memory hotplug.

As I understand, the later case could cause the timeout on non-preemptible
kernels.

My understanding, is that the same logic was used here when cond_resched()s
were added.

Please correct me if I am wrong.

Thank you,
Pavel