On Thu, 24 Nov 2011, Mel Gorman wrote: > > Calling alloc_pages_exact_node() means the allocation only passes the > > zonelist of a single node into the page allocator. If that node isn't > > online, it's zonelist may never have been initialized causing a strange > > oops that may not immediately be clear. > > > > I recently debugged an issue where node 0 wasn't online and an allocator > > was passing 0 to alloc_pages_exact_node() and it resulted in a NULL > > pointer on zonelist->_zoneref. If CONFIG_DEBUG_VM is enabled, though, it > > would be nice to catch this a bit earlier. > > > > Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx> > > Acked-by: Mel Gorman <mgorman@xxxxxxx> > > Out of curiousity, who was passing in the ID of an offline node to > alloc_pages_exact_node() ? > It was the block layer in blk_throtl_init() because it passes the ->node field of request_queue to the slab layer which uses alloc_pages_exact_node() and requeue_queue is allocated with __GFP_ZERO and ->node isn't initialized until later. At the same time, the machine only has a single node online, node 1, where the crashkernel was allocated. My analysis is at http://marc.info/?l=linux-kernel&m=132195611123426 I've worked with kernels without a node 0 very successfully since about 2.6.18 so the VM appears pretty stable in that regard, too, which is good news. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>