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

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Message-ID: <dfc0014a-9b85-5eeb-70ea-d622ccf5d988@redhat.com>
Date:   Wed, 1 Apr 2020 17:50:22 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>,
        Shile Zhang <shile.zhang@...ux.alibaba.com>
Cc:     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 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.

-- 
Thanks,

David / dhildenb