On Thu, Apr 06, 2017 at 06:21:55PM +0200, Michal Hocko wrote: > > This was my first time using your git branch instead of applying the patches > > from this thread to v4.11-rc5 myself. > > OK, so this looks like another thing to resolve. I have seen this > warning as well but I didn't consider it relevant because I had to tweak > the code make the node go offline (removed check_and_unmap_cpu_on_node > from try_offline_node) so I thought it was a fallout from there. > > But let's have a look. hotadd_new_pgdat does for an existing pgdat > /* Reset the nr_zones, order and classzone_idx before reuse */ > pgdat->nr_zones = 0; > pgdat->kswapd_order = 0; > pgdat->kswapd_classzone_idx = MAX_NR_ZONES; > > so free_area_init_node absolutely has to hit this warning. This is not > in the Linus tree because it is still in Andrew's mmotm coming from > http://www.ozlabs.org/~akpm/mmotm/broken-out/mm-vmscan-prevent-kswapd-sleeping-prematurely-due-to-mismatched-classzone_idx.patch > > So yay, finally that doesn't come from me. Mel, I guess that either > hotadd_new_pgdat should keep its kswapd_classzone_idx = 0 or the warning > should be updated. > Actually, it's obvious very quickly when I started the fix that updating the warning would then trigger on normal boot. It's more appropriate to let a hotadd of a new pgdat defer the initialisation of that field to kswapd starting for the new node. Can you try this? It's build/boot tested only, no hotplug testing. ---8<--- mm, vmscan: prevent kswapd sleeping prematurely due to mismatched classzone_idx -fix The patch "mm, vmscan: prevent kswapd sleeping prematurely due to mismatched classzone_idx" has different initial starting conditions when kswapd is asleep. kswapd initialises it properly when it starts but the patch initialises kswapd_classzone_idx early and trips on a warning in free_area_init_node. This patch leaves the kswapd_classzone_idx as zero and defers to kswapd to initialise it properly when it starts. This is a fix to the mmotm patch mm-vmscan-prevent-kswapd-sleeping-prematurely-due-to-mismatched-classzone_idx.patch Signed-off-by: Mel Gorman <mgorman@xxxxxxx> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 2309a7fbec93..76d4745513ee 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1214,10 +1214,14 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start) arch_refresh_nodedata(nid, pgdat); } else { - /* Reset the nr_zones, order and classzone_idx before reuse */ + /* + * Reset the nr_zones, order and classzone_idx before reuse. + * Note that kswapd will init kswapd_classzone_idx properly + * when it starts in the near future. + */ pgdat->nr_zones = 0; pgdat->kswapd_order = 0; - pgdat->kswapd_classzone_idx = MAX_NR_ZONES; + pgdat->kswapd_classzone_idx = 0; } /* we can use NODE_DATA(nid) from here */ -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
