Messages in this thread | | | Date | Wed, 4 Mar 2015 17:53:29 +0900 | From | Kamezawa Hiroyuki <> | Subject | Re: node-hotplug: is memset 0 safe in try_offline_node()? |
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On 2015/03/04 17:03, Xishi Qiu wrote: > On 2015/3/4 11:56, Gu Zheng wrote: > >> Hi Xishi, >> On 03/04/2015 10:52 AM, Xishi Qiu wrote: >> >>> On 2015/3/4 10:22, Xishi Qiu wrote: >>> >>>> On 2015/3/3 18:20, Gu Zheng wrote: >>>> >>>>> Hi Xishi, >>>>> On 03/03/2015 11:30 AM, Xishi Qiu wrote: >>>>> >>>>>> When hot-remove a numa node, we will clear pgdat, >>>>>> but is memset 0 safe in try_offline_node()? >>>>> >>>>> It is not safe here. In fact, this is a temporary solution here. >>>>> As you know, pgdat is accessed lock-less now, so protection >>>>> mechanism (RCU?) is needed to make it completely safe here, >>>>> but it seems a bit over-kill. >>>>> >>> >>> Hi Gu, >>> >>> Can we just remove "memset(pgdat, 0, sizeof(*pgdat));" ? >>> I find this will be fine in the stress test except the warning >>> when hot-add memory. >> >> As you see, it will trigger the warning in free_area_init_node(). >> Could you try the following patch? It will reset the pgdat before reuse it. >> >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >> index 1778628..0717649 100644 >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -1092,6 +1092,9 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start) >> return NULL; >> >> arch_refresh_nodedata(nid, pgdat); >> + } else { >> + /* Reset the pgdat to reuse */ >> + memset(pgdat, 0, sizeof(*pgdat)); >> } > > Hi Gu, > > If schedule last a long time, next_zone may be still access the pgdat here, > so it is not safe enough, right? >
How about just reseting pgdat->nr_zones and pgdat->classzone_idx to be 0 rather than memset() ?
It seems breaking pointer information in pgdat is not a choice. Just proper "values" should be reset.
Thanks, -Kame
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