> On Oct 9, 2015, at 5:02 PM, Jarno Rajahalme <jrajaha...@nicira.com> wrote: > > >> On Oct 9, 2015, at 3:11 PM, Jesse Gross <je...@nicira.com >> <mailto:je...@nicira.com>> wrote: >> >> On Fri, Oct 9, 2015 at 8:54 AM, Jarno Rajahalme <jrajaha...@nicira.com >> <mailto:jrajaha...@nicira.com>> wrote: >>> >>> On Oct 8, 2015, at 4:03 PM, Jesse Gross <je...@nicira.com >>> <mailto:je...@nicira.com>> wrote: >>> >>> On Wed, Oct 7, 2015 at 10:47 AM, Jarno Rajahalme <jrajaha...@nicira.com >>> <mailto:jrajaha...@nicira.com>> >>> wrote: >>> >>> >>> On Oct 6, 2015, at 6:01 PM, Jesse Gross <je...@nicira.com >>> <mailto:je...@nicira.com>> wrote: >>> >>> On Mon, Oct 5, 2015 at 1:25 PM, Alexander Duyck >>> <alexander.du...@gmail.com <mailto:alexander.du...@gmail.com>> wrote: >>> >>> On 10/05/2015 06:59 AM, Vlastimil Babka wrote: >>> >>> >>> On 10/02/2015 12:18 PM, Konstantin Khlebnikov wrote: >>> >>> >>> When openvswitch tries allocate memory from offline numa node 0: >>> stats = kmem_cache_alloc_node(flow_stats_cache, GFP_KERNEL | __GFP_ZERO, >>> 0) >>> It catches VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES || !node_online(nid)) >>> [ replaced with VM_WARN_ON(!node_online(nid)) recently ] in linux/gfp.h >>> This patch disables numa affinity in this case. >>> >>> Signed-off-by: Konstantin Khlebnikov <khlebni...@yandex-team.ru >>> <mailto:khlebni...@yandex-team.ru>> >>> >>> >>> >>> ... >>> >>> diff --git a/net/openvswitch/flow_table.c b/net/openvswitch/flow_table.c >>> index f2ea83ba4763..c7f74aab34b9 100644 >>> --- a/net/openvswitch/flow_table.c >>> +++ b/net/openvswitch/flow_table.c >>> @@ -93,7 +93,8 @@ struct sw_flow *ovs_flow_alloc(void) >>> >>> /* Initialize the default stat node. */ >>> stats = kmem_cache_alloc_node(flow_stats_cache, >>> - GFP_KERNEL | __GFP_ZERO, 0); >>> + GFP_KERNEL | __GFP_ZERO, >>> + node_online(0) ? 0 : NUMA_NO_NODE); >>> >>> >>> >>> Stupid question: can node 0 become offline between this check, and the >>> VM_WARN_ON? :) BTW what kind of system has node 0 offline? >>> >>> >>> >>> Another question to ask would be is it possible for node 0 to be online, but >>> be a memoryless node? >>> >>> I would say you are better off just making this call kmem_cache_alloc. I >>> don't see anything that indicates the memory has to come from node 0, so >>> adding the extra overhead doesn't provide any value. >>> >>> >>> I agree that this at least makes me wonder, though I actually have >>> concerns in the opposite direction - I see assumptions about this >>> being on node 0 in net/openvswitch/flow.c. >>> >>> Jarno, since you original wrote this code, can you take a look to see >>> if everything still makes sense? >>> >>> >>> We keep the pre-allocated stats node at array index 0, which is initially >>> used by all CPUs, but if CPUs from multiple numa nodes start updating the >>> stats, we allocate additional stats nodes (up to one per numa node), and the >>> CPUs on node 0 keep using the preallocated entry. If stats cannot be >>> allocated from CPUs local node, then those CPUs keep using the entry at >>> index 0. Currently the code in net/openvswitch/flow.c will try to allocate >>> the local memory repeatedly, which may not be optimal when there is no >>> memory at the local node. >>> >>> Allocating the memory for the index 0 from other than node 0, as discussed >>> here, just means that the CPUs on node 0 will keep on using non-local memory >>> for stats. In a scenario where there are CPUs on two nodes (0, 1), but only >>> the node 1 has memory, a shared flow entry will still end up having separate >>> memory allocated for both nodes, but both of the nodes would be at node 1. >>> However, there is still a high likelihood that the memory allocations would >>> not share a cache line, which should prevent the nodes from invalidating >>> each other’s caches. Based on this I do not see a problem relaxing the >>> memory allocation for the default stats node. If node 0 has memory, however, >>> it would be better to allocate the memory from node 0. >>> >>> >>> Thanks for going through all of that. >>> >>> It seems like the question that is being raised is whether it actually >>> makes sense to try to get the initial memory on node 0, especially >>> since it seems to introduce some corner cases? Is there any reason why >>> the flow is more likely to hit node 0 than a randomly chosen one? >>> (Assuming that this is a multinode system, otherwise it's kind of a >>> moot point.) We could have a separate pointer to the default allocated >>> memory, so it wouldn't conflict with memory that was intentionally >>> allocated for node 0. >>> >>> >>> It would still be preferable to know from which node the default stats node >>> was allocated, and store it in the appropriate pointer in the array. We >>> could then add a new “default stats node index” that would be used to locate >>> the node in the array of pointers we already have. That way we would avoid >>> extra allocation and processing of the default stats node. >> >> I agree, that sounds reasonable to me. Will you make that change? >> >> Besides eliminating corner cases, it might help performance in some >> cases too by avoiding stressing memory bandwidth on node 0. >
According to the comment above kmem_cache_alloc_node(), kmem_cache_alloc_node() should not BUG_ON/WARN_ON in this case: > /** > * kmem_cache_alloc_node - Allocate an object on the specified node > * @cachep: The cache to allocate from. > * @flags: See kmalloc(). > * @nodeid: node number of the target node. > * > * Identical to kmem_cache_alloc but it will allocate memory on the given > * node, which can improve the performance for cpu bound structures. > * > * Fallback to other node is possible if __GFP_THISNODE is not set. > */ See also this from cpuset.c: > /** > * cpuset_mem_spread_node() - On which node to begin search for a file page > * cpuset_slab_spread_node() - On which node to begin search for a slab page > * > * If a task is marked PF_SPREAD_PAGE or PF_SPREAD_SLAB (as for > * tasks in a cpuset with is_spread_page or is_spread_slab set), > * and if the memory allocation used cpuset_mem_spread_node() > * to determine on which node to start looking, as it will for > * certain page cache or slab cache pages such as used for file > * system buffers and inode caches, then instead of starting on the > * local node to look for a free page, rather spread the starting > * node around the tasks mems_allowed nodes. > * > * We don't have to worry about the returned node being offline > * because "it can't happen", and even if it did, it would be ok. > * > * The routines calling guarantee_online_mems() are careful to > * only set nodes in task->mems_allowed that are online. So it > * should not be possible for the following code to return an > * offline node. But if it did, that would be ok, as this routine > * is not returning the node where the allocation must be, only > * the node where the search should start. The zonelist passed to > * __alloc_pages() will include all nodes. If the slab allocator > * is passed an offline node, it will fall back to the local node. > * See kmem_cache_alloc_node(). > */ Based on this it seems this is a bug in the memory allocator, it probably should not be calling alloc_pages_exact_node() when __GFP_THISNODE is not set? Jarno _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
