IRQs are left disabled for the zone and node VM event counters. On some
architectures this is unnecessary and it confuses what the scope of the
locking for per-cpu lists and VM counters are.
This patch reduces the scope of IRQs being disabled via local_[lock|unlock]
and relies on preemption disabling for the per-cpu counters. This
is not completely free on all architectures as architectures
without HAVE_CMPXCHG_DOUBLE will disable/enable IRQs again for the
mod_zone_freepage_state call. However, it clarifies what the per-cpu
pages lock protects and how zone stats may need IRQs disabled if ever
called from an IRQ context.
Signed-off-by: Mel Gorman <[email protected]>
---
mm/page_alloc.c | 22 ++++++++++++++++------
1 file changed, 16 insertions(+), 6 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 32c64839c145..25d9351e75d8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3461,11 +3461,17 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone,
pcp = this_cpu_ptr(zone->per_cpu_pageset);
list = &pcp->lists[migratetype];
page = __rmqueue_pcplist(zone, migratetype, alloc_flags, pcp, list);
+ local_unlock_irqrestore(&pagesets.lock, flags);
if (page) {
+ /*
+ * per-cpu counter updates are not preempt-safe but is
+ * acceptable to race versus interrupts.
+ */
+ preempt_disable();
__count_zid_vm_events(PGALLOC, page_zonenum(page), 1);
zone_statistics(preferred_zone, zone, 1);
+ preempt_enable();
}
- local_unlock_irqrestore(&pagesets.lock, flags);
return page;
}
@@ -3517,15 +3523,17 @@ struct page *rmqueue(struct zone *preferred_zone,
if (!page)
page = __rmqueue(zone, order, migratetype, alloc_flags);
} while (page && check_new_pages(page, order));
- spin_unlock(&zone->lock);
+ spin_unlock_irqrestore(&zone->lock, flags);
+
if (!page)
goto failed;
+
+ preempt_disable();
__mod_zone_freepage_state(zone, -(1 << order),
get_pcppage_migratetype(page));
-
__count_zid_vm_events(PGALLOC, page_zonenum(page), 1 << order);
zone_statistics(preferred_zone, zone, 1);
- local_irq_restore(flags);
+ preempt_enable();
out:
/* Separate test+clear to avoid unnecessary atomics */
@@ -5090,10 +5098,12 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
nr_populated++;
}
+ local_unlock_irqrestore(&pagesets.lock, flags);
+
+ preempt_disable();
__count_zid_vm_events(PGALLOC, zone_idx(zone), nr_account);
zone_statistics(ac.preferred_zoneref->zone, zone, nr_account);
-
- local_unlock_irqrestore(&pagesets.lock, flags);
+ preempt_enable();
return nr_populated;
--
2.26.2