[RFC:Patch: 003/008](memory hotplug) check node online in __alloc_pages

[Yasunori Goto <y-goto@jp.fujitsu.com>]

This is to add pgdat_remove_read_lock()/unlock() for parsing zonelist in
__alloc_pages_internal().
The node might be removed before pgdat_remove_read_lock(),
node_online() must be checked at first. If offlined, don't parse it.

Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>

---
 mm/page_alloc.c |   36 ++++++++++++++++++++++++++++++++++--
 1 file changed, 34 insertions(+), 2 deletions(-)

Index: current/mm/page_alloc.c
===================================================================
--- current.orig/mm/page_alloc.c	2008-07-31 19:01:46.000000000 +0900
+++ current/mm/page_alloc.c	2008-07-31 19:19:19.000000000 +0900
@@ -1394,10 +1394,22 @@ get_page_from_freelist(gfp_t gfp_mask, n
 	int zlc_active = 0;		/* set if using zonelist_cache */
 	int did_zlc_setup = 0;		/* just call zlc_setup() one time */
 
+	pgdat_remove_read_lock();
+	if (unlikely(!node_online(zonelist_nid))) {
+		/*
+		 * Pgdat removing worked before here.
+		 * Don't touch pgdat/zone/zonelist any more.
+		 */
+		pgdat_remove_read_unlock();
+		return NULL;
+	}
+
 	(void)first_zones_zonelist(zonelist, high_zoneidx, nodemask,
 							&preferred_zone);
-	if (!preferred_zone)
+	if (!preferred_zone) {
+		pgdat_remove_read_unlock();
 		return NULL;
+	}
 
 	classzone_idx = zone_idx(preferred_zone);
 
@@ -1451,6 +1463,7 @@ try_next_zone:
 		zlc_active = 0;
 		goto zonelist_scan;
 	}
+	pgdat_remove_read_unlock();
 	return page;
 }
 
@@ -1536,10 +1549,21 @@ __alloc_pages_internal(gfp_t gfp_mask, u
 		return NULL;
 
 restart:
+	pgdat_remove_read_lock();
+	if (unlikely(!node_online(zonelist_nid))) {
+		/*
+		 * pgdat removing worked before here.
+		 * zone & zonelist can't be touched.
+		 */
+		pgdat_remove_read_unlock();
+		goto nopage;
+	}
 	zonelist = node_zonelist(zonelist_nid, gfp_mask);;
 	z = zonelist->_zonerefs;  /* the list of zones suitable for gfp_mask */
+	zone = z->zone;
+	pgdat_remove_read_unlock();
 
-	if (unlikely(!z->zone)) {
+	if (unlikely(!zone)) {
 		/*
 		 * Happens if we have an empty zonelist as a result of
 		 * GFP_THISNODE being used on a memoryless node
@@ -1565,9 +1589,17 @@ restart:
 	if (NUMA_BUILD && (gfp_mask & GFP_THISNODE) == GFP_THISNODE)
 		goto nopage;
 
+	pgdat_remove_read_lock();
+
+	if (unlikely(!node_online(zonelist_nid))) {
+		pgdat_remove_read_unlock();
+		goto nopage;
+	}
 	for_each_zone_zonelist(zone, z, zonelist, high_zoneidx)
 		wakeup_kswapd(zone, order);
 
+	pgdat_remove_read_unlock();
+
 	/*
 	 * OK, we're below the kswapd watermark and have kicked background
 	 * reclaim. Now things get more complex, so set up alloc_flags according

-- 
Yasunori Goto 


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