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    SubjectRe: [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

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