linux-kernel - [PATCH 09/14] mm: meminit: Minimise number of pfn->page lookups during initialisation

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Date:	Mon, 13 Apr 2015 11:17:01 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Linux-MM <linux-mm@...ck.org>
Cc:	Robin Holt <holt@....com>, Nathan Zimmer <nzimmer@....com>,
	Daniel Rahn <drahn@...e.com>,
	Davidlohr Bueso <dbueso@...e.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Tom Vaden <tom.vaden@...com>,
	Scott Norton <scott.norton@...com>,
	LKML <linux-kernel@...r.kernel.org>, Mel Gorman <mgorman@...e.de>
Subject: [PATCH 09/14] mm: meminit: Minimise number of pfn->page lookups during initialisation

Deferred memory initialisation is using pfn_to_page() on every PFN
unnecessarily. This patch minimises the number of lookups and scheduler
checks.

Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 mm/page_alloc.c | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 10ba841c7609..21bb818aa3c4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1077,6 +1077,7 @@ void __defermem_init deferred_init_memmap(int nid)
 
 		for_each_mem_pfn_range(i, nid, &walk_start, &walk_end, NULL) {
 			unsigned long pfn, end_pfn;
+			struct page *page = NULL;
 
 			end_pfn = min(walk_end, zone_end_pfn(zone));
 			pfn = first_init_pfn;
@@ -1086,13 +1087,32 @@ void __defermem_init deferred_init_memmap(int nid)
 				pfn = zone->zone_start_pfn;
 
 			for (; pfn < end_pfn; pfn++) {
-				struct page *page;
-
-				if (!pfn_valid(pfn))
+				if (!pfn_valid_within(pfn))
 					continue;
 
-				if (!meminit_pfn_in_nid(pfn, nid, &nid_init_state))
+				/*
+				 * Ensure pfn_valid is checked every
+				 * MAX_ORDER_NR_PAGES for memory holes
+				 */
+				if ((pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
+					if (!pfn_valid(pfn)) {
+						page = NULL;
+						continue;
+					}
+				}
+
+				if (!meminit_pfn_in_nid(pfn, nid, &nid_init_state)) {
+					page = NULL;
 					continue;
+				}
+
+				/* Minimise pfn page lookups and scheduler checks */
+				if (page && (pfn & (MAX_ORDER_NR_PAGES - 1)) != 0) {
+					page++;
+				} else {
+					page = pfn_to_page(pfn);
+					cond_resched();
+				}
 
 				if (page->flags) {
 					VM_BUG_ON(page_zone(page) != zone);
@@ -1101,7 +1121,6 @@ void __defermem_init deferred_init_memmap(int nid)
 
 				__init_single_page(page, pfn, zid, nid);
 				__free_pages_boot_core(page, pfn, 0);
-				cond_resched();
 			}
 			first_init_pfn = max(end_pfn, first_init_pfn);
 		}
-- 
2.1.2

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