Date:   Wed, 11 Mar 2020 13:45:04 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Shile Zhang <shile.zhang@...ux.alibaba.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] mm: fix tick timer stall during deferred page init

On Wed, Mar 11, 2020 at 8:39 AM Shile Zhang
<shile.zhang@...ux.alibaba.com> 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

Sorry for joining late to this thread. I wonder if we could use
sched_clock() to print this statistics. Or not to print statistics at
all?

==============
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3c4eb750a199..5958f599aced 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1770,7 +1770,7 @@ static int __init deferred_init_memmap(void *data)
        const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
        unsigned long spfn = 0, epfn = 0, nr_pages = 0;
        unsigned long first_init_pfn, flags;
-       unsigned long start = jiffies;
+       unsigned long start = sched_clock();
        struct zone *zone;
        int zid;
        u64 i;
@@ -1817,8 +1817,8 @@ static int __init deferred_init_memmap(void *data)
        /* Sanity check that the next zone really is unpopulated */
        WARN_ON(++zid < MAX_NR_ZONES && populated_zone(++zone));

-       pr_info("node %d initialised, %lu pages in %ums\n",
-               pgdat->node_id, nr_pages, jiffies_to_msecs(jiffies - start));
+       pr_info("node %d initialised, %lu pages in %lldns\n",
+               pgdat->node_id, nr_pages, sched_clock() - start);

        pgdat_init_report_one_done();
        return 0;
==============

[    1.245331] node 0 initialised, 10256176 pages in 373565742ns

Pasha



> Fixes: 3a2d7fa8a3d5 ("mm: disable interrupts while initializing deferred pages").
>
> Co-developed-by: Kirill Tkhai <ktkhai@...tuozzo.com>
> Signed-off-by: Kirill Tkhai <ktkhai@...tuozzo.com>
> Signed-off-by: Shile Zhang <shile.zhang@...ux.alibaba.com>
> ---
>  mm/page_alloc.c | 25 ++++++++++++++++++++++---
>  1 file changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3c4eb750a199..a3a47845e150 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1763,12 +1763,17 @@ deferred_init_maxorder(u64 *i, struct zone *zone, unsigned long *start_pfn,
>         return nr_pages;
>  }
>
> +/*
> + * Release the pending interrupts for every TICK_PAGE_COUNT pages.
> + */
> +#define TICK_PAGE_COUNT        (32 * 1024)
> +
>  /* Initialise remaining memory on a node */
>  static int __init deferred_init_memmap(void *data)
>  {
>         pg_data_t *pgdat = data;
>         const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
> -       unsigned long spfn = 0, epfn = 0, nr_pages = 0;
> +       unsigned long spfn = 0, epfn = 0, nr_pages = 0, prev_nr_pages = 0;
>         unsigned long first_init_pfn, flags;
>         unsigned long start = jiffies;
>         struct zone *zone;
> @@ -1779,6 +1784,7 @@ static int __init deferred_init_memmap(void *data)
>         if (!cpumask_empty(cpumask))
>                 set_cpus_allowed_ptr(current, cpumask);
>
> +again:
>         pgdat_resize_lock(pgdat, &flags);
>         first_init_pfn = pgdat->first_deferred_pfn;
>         if (first_init_pfn == ULONG_MAX) {
> @@ -1790,7 +1796,6 @@ static int __init deferred_init_memmap(void *data)
>         /* Sanity check boundaries */
>         BUG_ON(pgdat->first_deferred_pfn < pgdat->node_start_pfn);
>         BUG_ON(pgdat->first_deferred_pfn > pgdat_end_pfn(pgdat));
> -       pgdat->first_deferred_pfn = ULONG_MAX;
>
>         /* Only the highest zone is deferred so find it */
>         for (zid = 0; zid < MAX_NR_ZONES; zid++) {
> @@ -1809,9 +1814,23 @@ static int __init deferred_init_memmap(void *data)
>          * that we can avoid introducing any issues with the buddy
>          * allocator.
>          */
> -       while (spfn < epfn)
> +       while (spfn < epfn) {
>                 nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
> +               /*
> +                * Release the interrupts for every TICK_PAGE_COUNT pages
> +                * (128MB) to give tick timer the chance to update the
> +                * system jiffies.
> +                */
> +               if ((nr_pages - prev_nr_pages) > TICK_PAGE_COUNT) {
> +                       prev_nr_pages = nr_pages;
> +                       pgdat->first_deferred_pfn = spfn;
> +                       pgdat_resize_unlock(pgdat, &flags);
> +                       goto again;
> +               }
> +       }
> +
>  zone_empty:
> +       pgdat->first_deferred_pfn = ULONG_MAX;
>         pgdat_resize_unlock(pgdat, &flags);
>
>         /* Sanity check that the next zone really is unpopulated */
> --
> 2.24.0.rc2
>

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