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From: Daniel Jordan <daniel.m.jordan@oracle.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: David Hildenbrand <david@redhat.com>,
	Shile Zhang <shile.zhang@linux.alibaba.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Kirill Tkhai <ktkhai@virtuozzo.com>,
	Pavel Tatashin <pasha.tatashin@soleen.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] mm: fix tick timer stall during deferred page init
Date: Wed, 1 Apr 2020 12:09:29 -0400	[thread overview]
Message-ID: <20200401160929.jwekhr24tb44odea@ca-dmjordan1.us.oracle.com> (raw)
In-Reply-To: <20200401160048.GU22681@dhcp22.suse.cz>

On Wed, Apr 01, 2020 at 06:00:48PM +0200, Michal Hocko wrote:
> On Wed 01-04-20 17:50:22, David Hildenbrand wrote:
> > On 01.04.20 17:42, Michal Hocko wrote:
> > > I am sorry but I have completely missed this patch.
> > > 
> > > On Wed 11-03-20 20:38:48, Shile Zhang wrote:
> > >> When 'CONFIG_DEFERRED_STRUCT_PAGE_INIT' is set, 'pgdatinit' kthread will
> > >> initialise the deferred pages with local interrupts disabled. It is
> > >> introduced by commit 3a2d7fa8a3d5 ("mm: disable interrupts while
> > >> initializing deferred pages").
> > >>
> > >> On machine with NCPUS <= 2, the 'pgdatinit' kthread could be bound to
> > >> the boot CPU, which could caused the tick timer long time stall, system
> > >> jiffies not be updated in time.
> > >>
> > >> The dmesg shown that:
> > >>
> > >>     [    0.197975] node 0 initialised, 32170688 pages in 1ms
> > >>
> > >> Obviously, 1ms is unreasonable.
> > >>
> > >> Now, fix it by restore in the pending interrupts for every 32*1204 pages
> > >> (128MB) initialized, give the chance to update the systemd jiffies.
> > >> The reasonable demsg shown likes:
> > >>
> > >>     [    1.069306] node 0 initialised, 32203456 pages in 894ms
> > >>
> > >> Fixes: 3a2d7fa8a3d5 ("mm: disable interrupts while initializing deferred pages").
> > > 
> > > I dislike this solution TBH. It effectivelly conserves the current code
> > > and just works around the problem. Why do we hold the IRQ lock here in
> > > the first place? This is an early init code and a very limited code is
> > > running at this stage. Certainly nothing memory hotplug related which
> > > should be the only path really interested in the resize lock AFAIR.
> > 
> > Yeah, I don't think ACPI and friends are up yet.
> 
> Just to save somebody time to check. The deferred initialization blocks
> the further boot until all workders are done - see page_alloc_init_late
> (kernel_init path).

Ha, I just finished following all the hotplug paths to check this out, and as
you all know there are a *lot* :-) Well at least we're in agreement.

> > > This needs a double checking but I strongly believe that the lock can be
> > > simply dropped in this path.

This is what my fix does, it limits the time the resize lock is held.


  reply	other threads:[~2020-04-01 16:09 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-11 12:38 [PATCH v3] mm: fix tick timer stall during deferred page init Shile Zhang
2020-03-11 17:45 ` Pavel Tatashin
2020-03-11 20:16   ` Kirill Tkhai
2020-03-11 20:25     ` Pavel Tatashin
2020-03-19 19:05 ` Daniel Jordan
2020-03-26 18:58   ` Daniel Jordan
2020-03-26 19:36     ` Pavel Tatashin
2020-03-27  4:39       ` Shile Zhang
2020-03-28  0:17         ` Daniel Jordan
2020-04-01 14:26 ` David Hildenbrand
2020-04-01 15:42 ` Michal Hocko
2020-04-01 15:50   ` David Hildenbrand
2020-04-01 16:00     ` Michal Hocko
2020-04-01 16:09       ` Daniel Jordan [this message]
2020-04-01 16:12         ` Michal Hocko
2020-04-01 16:15           ` David Hildenbrand
2020-04-01 16:18           ` Daniel Jordan
2020-04-01 16:26             ` Michal Hocko
2020-04-01 16:41               ` Pavel Tatashin
2020-04-01 16:46                 ` Michal Hocko
2020-04-01 16:51                   ` Pavel Tatashin
2020-04-01 17:13                     ` Daniel Jordan

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