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

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Message-ID: <20180313194546.k62tni4g4gnds2nx@xakep.localdomain>
Date:   Tue, 13 Mar 2018 15:45:46 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        m.mizuma@...fujitsu.com, mhocko@...e.com, catalin.marinas@....com,
        takahiro.akashi@...aro.org, gi-oh.kim@...fitbricks.com,
        heiko.carstens@...ibm.com, baiyaowei@...s.chinamobile.com,
        richard.weiyang@...il.com, paul.burton@...s.com,
        miles.chen@...iatek.com, vbabka@...e.cz, mgorman@...e.de,
        hannes@...xchg.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [v5 1/2] mm: disable interrupts while initializing deferred pages

> > 
> > 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