Initializing struct pages is a long task and keeping interrupts disabled
for the duration of this operation introduces a number of problems.
1. jiffies are not updated for long period of time, and thus incorrect time
is reported. See proposed solution and discussion here:
lkml/20200311123848.118638-1-shile.zhang@xxxxxxxxxxxxxxxxx
2. It prevents farther improving deferred page initialization by allowing
inter-node multi-threading.
We are keeping interrupts disabled to solve a rather theoretical problem
that was never observed in real world (See 3a2d7fa8a3d5).
Lets keep interrupts enabled. In case we ever encounter a scenario where
an interrupt thread wants to allocate large amount of memory this early in
boot we can deal with that by growing zone (see deferred_grow_zone()) by
the needed amount before starting deferred_init_memmap() threads.
Before:
[ 1.232459] node 0 initialised, 12058412 pages in 1ms
After:
[ 1.632580] node 0 initialised, 12051227 pages in 436ms
Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
---
mm/page_alloc.c | 21 +++++++--------------
1 file changed, 7 insertions(+), 14 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3c4eb750a199..4498a13b372d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1792,6 +1792,13 @@ static int __init deferred_init_memmap(void *data)
BUG_ON(pgdat->first_deferred_pfn > pgdat_end_pfn(pgdat));
pgdat->first_deferred_pfn = ULONG_MAX;
+ /*
+ * Once we unlock here, the zone cannot be grown anymore, thus if an
+ * interrupt thread must allocate this early in boot, zone must be
+ * pre-grown prior to start of deferred page initialization.
+ */
+ pgdat_resize_unlock(pgdat, &flags);
+
/* Only the highest zone is deferred so find it */
for (zid = 0; zid < MAX_NR_ZONES; zid++) {
zone = pgdat->node_zones + zid;
@@ -1812,8 +1819,6 @@ static int __init deferred_init_memmap(void *data)
while (spfn < epfn)
nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
zone_empty:
- pgdat_resize_unlock(pgdat, &flags);
-
/* Sanity check that the next zone really is unpopulated */
WARN_ON(++zid < MAX_NR_ZONES && populated_zone(++zone));
@@ -1854,18 +1859,6 @@ deferred_grow_zone(struct zone *zone, unsigned int order)
return false;
pgdat_resize_lock(pgdat, &flags);
-
- /*
- * If deferred pages have been initialized while we were waiting for
- * the lock, return true, as the zone was grown. The caller will retry
- * this zone. We won't return to this function since the caller also
- * has this static branch.
- */
- if (!static_branch_unlikely(&deferred_pages)) {
- pgdat_resize_unlock(pgdat, &flags);
- return true;
- }
-
/*
* If someone grew this zone while we were waiting for spinlock, return
* true, as there might be enough pages already.
--
2.17.1
