On 2015/10/9 17:08, Kamezawa Hiroyuki wrote: > On 2015/10/09 14:52, Jiang Liu wrote: >> On 2015/10/9 4:20, Andrew Morton wrote: >>> On Wed, 19 Aug 2015 17:18:15 -0700 (PDT) David Rientjes >>> <rientjes@xxxxxxxxxx> wrote: >>> >>>> On Wed, 19 Aug 2015, Patil, Kiran wrote: >>>> >>>>> Acked-by: Kiran Patil <kiran.patil@xxxxxxxxx> >>>> >>>> Where's the call to preempt_disable() to prevent kernels with >>>> preemption >>>> from making numa_node_id() invalid during this iteration? >>> >>> David asked this question twice, received no answer and now the patch >>> is in the maintainer tree, destined for mainline. >>> >>> If I was asked this question I would respond >>> >>> The use of numa_mem_id() is racy and best-effort. If the unlikely >>> race occurs, the memory allocation will occur on the wrong node, the >>> overall result being very slightly suboptimal performance. The >>> existing use of numa_node_id() suffers from the same issue. >>> >>> But I'm not the person proposing the patch. Please don't just ignore >>> reviewer comments! >> Hi Andrew, >> Apologize for the slow response due to personal reasons! >> And thanks for answering the question from David. To be honest, >> I didn't know how to answer this question before. Actually this >> question has puzzled me for a long time when dealing with memory >> hot-removal. For normal cases, it only causes sub-optimal memory >> allocation if schedule event happens between querying NUMA node id >> and calling alloc_pages_node(). But what happens if system run into >> following execution sequence? >> 1) node = numa_mem_id(); >> 2) memory hot-removal event triggers >> 2.1) remove affected memory >> 2.2) reset pgdat to zero if node becomes empty after memory removal > > I'm sorry if I misunderstand something. > After commit b0dc3a342af36f95a68fe229b8f0f73552c5ca08, there is no > memset(). Hi Kamezawa, Thanks for the information. The commit solved the issue what I was puzzling about. With this change applied, thing should work as expected. Seems it would be better to enhance __build_all_zonelists() to handle those offlined empty nodes too, but that really doesn't make to much difference:) Thanks for the info again! Thanks! Gerry -- To unsubscribe from this list: send the line "unsubscribe linux-hotplug" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
