[PATCH 1/4] mm, page_owner: make init_pages_in_zone() faster

[Vlastimil Babka]

In init_pages_in_zone() we currently use the generic set_page_owner() function
to initialize page_owner info for early allocated pages. This means we
needlessly do lookup_page_ext() twice for each page, and more importantly
save_stack(), which has to unwind the stack and find the corresponding stack
depot handle. Because the stack is always the same for the initialization,
unwind it once in init_pages_in_zone() and reuse the handle. Also avoid the
repeated lookup_page_ext().

This can significantly reduce boot times with page_owner=on on large machines,
especially for kernels built without frame pointer, where the stack unwinding
is noticeably slower.

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
 mm/page_owner.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 401feb070335..5aa21ca237d9 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -183,6 +183,20 @@ noinline void __set_page_owner(struct page *page, unsigned int order,
 	__set_bit(PAGE_EXT_OWNER, &page_ext->flags);
 }
 
+static void __set_page_owner_init(struct page_ext *page_ext,
+					depot_stack_handle_t handle)
+{
+	struct page_owner *page_owner;
+
+	page_owner = get_page_owner(page_ext);
+	page_owner->handle = handle;
+	page_owner->order = 0;
+	page_owner->gfp_mask = 0;
+	page_owner->last_migrate_reason = -1;
+
+	__set_bit(PAGE_EXT_OWNER, &page_ext->flags);
+}
+
 void __set_page_owner_migrate_reason(struct page *page, int reason)
 {
 	struct page_ext *page_ext = lookup_page_ext(page);
@@ -520,10 +534,13 @@ static void init_pages_in_zone(pg_data_t *pgdat, struct zone *zone)
 	unsigned long pfn = zone->zone_start_pfn, block_end_pfn;
 	unsigned long end_pfn = pfn + zone->spanned_pages;
 	unsigned long count = 0;
+	depot_stack_handle_t init_handle;
 
 	/* Scan block by block. First and last block may be incomplete */
 	pfn = zone->zone_start_pfn;
 
+	init_handle = save_stack(0);
+
 	/*
 	 * Walk the zone in pageblock_nr_pages steps. If a page block spans
 	 * a zone boundary, it will be double counted between zones. This does
@@ -570,7 +587,7 @@ static void init_pages_in_zone(pg_data_t *pgdat, struct zone *zone)
 				continue;
 
 			/* Found early allocated page */
-			set_page_owner(page, 0, 0);
+			__set_page_owner_init(page_ext, init_handle);
 			count++;
 		}
 	}
-- 
2.13.2