linux-kernel - Re: [PATCH v3] mm: fix tick timer stall during deferred page init

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Date:   Wed, 1 Apr 2020 18:00:48 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Shile Zhang <shile.zhang@...ux.alibaba.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm: fix tick timer stall during deferred page init

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).
-- 
Michal Hocko
SUSE Labs