[PATCH v3] mm: fix tick timer stall during deferred page init

[Shile Zhang]

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").

Co-developed-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Signed-off-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Signed-off-by: Shile Zhang <shile.zhang@xxxxxxxxxxxxxxxxx>
---
 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