On 2015/4/20 9:42, Gu Zheng wrote: > Hi Xishi, > On 04/18/2015 04:05 AM, Yasuaki Ishimatsu wrote: > >> >> Your patches will fix your issue. >> But, if BIOS reports memory first at node hot add, pgdat can >> not be initialized. >> >> Memory hot add flows are as follows: >> >> add_memory >> ... >> -> hotadd_new_pgdat() >> ... >> -> node_set_online(nid) >> >> When calling hotadd_new_pgdat() for a hot added node, the node is >> offline because node_set_online() is not called yet. So if applying >> your patches, the pgdat is not initialized in this case. > > Ishimtasu's worry is reasonable. And I am afraid the fix here is a bit > over-kill. > >> >> Thanks, >> Yasuaki Ishimatsu >> >> On Fri, 17 Apr 2015 18:50:32 +0800 >> Xishi Qiu <qiuxishi@xxxxxxxxxx> wrote: >> >>> Hot remove nodeXX, then hot add nodeXX. If BIOS report cpu first, it will call >>> hotadd_new_pgdat(nid, 0), this will set pgdat->node_start_pfn to 0. As nodeXX >>> exists at boot time, so pgdat->node_spanned_pages is the same as original. Then >>> free_area_init_core()->memmap_init() will pass a wrong start and a nonzero size. > > As your analysis said the root cause here is passing a *0* as the node_start_pfn, > then the chaos occurred when init the zones. And this only happens to the re-hotadd > node, so how about using the saved *node_start_pfn* (via get_pfn_range_for_nid(nid, &start_pfn, &end_pfn)) > instead if we find "pgdat->node_start_pfn == 0 && !node_online(XXX)"? > > Thanks, > Gu > Hi Gu, I first considered this method, but if the hot added node's start and size are different from before, it makes the chaos. e.g. nodeXX (8-16G) remove nodeXX BIOS report cpu first and online it hotadd nodeXX use the original value, so pgdat->node_start_pfn is set to 8G, and size is 8G BIOS report mem(10-12G) call add_memory()->__add_zone()->grow_zone_span()/grow_pgdat_span() the start is still 8G, not 10G, this is chaos! Thanks, Xishi Qiu -- 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>