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
intra-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
Fixes: 3a2d7fa8a3d5 ("mm: disable interrupts while initializing deferred pages")
Cc: stable@xxxxxxxxxxxxxxx # 4.17+
Reported-by: Shile Zhang <shile.zhang@xxxxxxxxxxxxxxxxx>
Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
---
include/linux/mmzone.h | 2 ++
mm/page_alloc.c | 22 ++++++++--------------
2 files changed, 10 insertions(+), 14 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 462f6873905a..c5bdf55da034 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -721,6 +721,8 @@ typedef struct pglist_data {
/*
* Must be held any time you expect node_start_pfn,
* node_present_pages, node_spanned_pages or nr_zones to stay constant.
+ * Also synchronizes pgdat->first_deferred_pfn during deferred page
+ * init.
*
* pgdat_resize_lock() and pgdat_resize_unlock() are provided to
* manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e8ff6a176164..68669d3a5a66 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1790,6 +1790,13 @@ 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;
@@ -1809,11 +1816,9 @@ static int __init deferred_init_memmap(void *data)
*/
while (spfn < epfn) {
nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
- touch_nmi_watchdog();
+ cond_resched();
}
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));
@@ -1855,17 +1860,6 @@ deferred_grow_zone(struct zone *zone, unsigned int order)
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
