On Thu 06-04-17 17:55:20, Mel Gorman wrote: > 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. It will start during the online phase which is later than this physical memory hotadd. > 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> Yes, that is what I would expect. Feel free to add Acked-by: Michal Hocko <mhocko@xxxxxxxx> if this is routed as a separate patch. Although I expect Andrew will fold it into the original patch. > 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> -- Michal Hocko SUSE Labs -- 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>
