mm, page_owner: don't grab zone->lock for init_pages_in_zone() (10903027) · Commits · 戴 / test

init_pages_in_zone() is run under zone->lock, which means a long lock time and disabled interrupts on large machines. This is currently not an issue since it runs early in boot, but a later patch will change that. However, like other pfn scanners, we don't actually need zone->lock even when other cpus are running. The only potentially dangerous operation here is reading bogus buddy page owner due to race, and we already know how to handle that. The worst that can happen is that we skip some early allocated pages, which should not affect the debugging power of page_owner noticeably. Link: http://lkml.kernel.org/r/20170720134029.25268-4-vbabka@suse.cz Signed-off-by:

Vlastimil Babka <vbabka@suse.cz> Acked-by:

Michal Hocko <mhocko@suse.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Yang Shi <yang.shi@linaro.org> Cc: Laura Abbott <labbott@redhat.com> Cc: Vinayak Menon <vinmenon@codeaurora.org> Cc: zhong jiang <zhongjiang@huawei.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/page_owner.c

+10 −6

Original line number	Diff line number	Diff line
		@@ -562,11 +562,17 @@ static void init_pages_in_zone(pg_data_t pgdat, struct zone zone)
		continue;

		/*
		* We are safe to check buddy flag and order, because
		* this is init stage and only single thread runs.
		* To avoid having to grab zone->lock, be a little
		* careful when reading buddy page order. The only
		* danger is that we skip too much and potentially miss
		* some early allocated pages, which is better than
		* heavy lock contention.
		*/
		if (PageBuddy(page)) {
		pfn += (1UL << page_order(page)) - 1;
		unsigned long order = page_order_unsafe(page);

		if (order > 0 && order < MAX_ORDER)
		pfn += (1UL << order) - 1;
		continue;
		}

		@@ -585,6 +591,7 @@ static void init_pages_in_zone(pg_data_t pgdat, struct zone zone)
		__set_page_owner_handle(page_ext, early_handle, 0, 0);
		count++;
		}
		cond_resched();
		}

		pr_info("Node %d, zone %8s: page owner found early allocated %lu pages\n",
		@@ -595,15 +602,12 @@ static void init_zones_in_node(pg_data_t *pgdat)
		{
		struct zone *zone;
		struct zone *node_zones = pgdat->node_zones;
		unsigned long flags;

		for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
		if (!populated_zone(zone))
		continue;

		spin_lock_irqsave(&zone->lock, flags);
		init_pages_in_zone(pgdat, zone);
		spin_unlock_irqrestore(&zone->lock, flags);
		}
		}

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