Hi Michal and Mel, To reproduce the issue, I specified the large trace buffer. The issue also occurs with trace_buf_size=12M and movable_node on 4.14.0.
In my system, there are 384 CPUs and 8 nodes. So when not using movable_node boot option, kernel can use about 16GB memory for trace buffer. So Kernel boots up with trace_buf_size=12M. But when using movable_node, 6 nodes are managed as MOVABLE_ZONE in my system and kernel can use only about 4GB memory for trace buffer. So memory allocation failure of trace buffer occurs with trace_buf_size=12M and movable_node. I don't know you still think 12M is large. But the latest Fujitsu server supports 448 CPUs. The issue may occur with trace_buf_size=10M on the system. Additionally the number of CPU in a server is increasing year by year. So the issue will occurs even if we don't specify large trace buffer. Thanks, Yasuaki Ishimatsu On 11/15/2017 09:57 AM, Michal Hocko wrote: > On Wed 15-11-17 14:43:14, Mel Gorman wrote: >> On Wed, Nov 15, 2017 at 03:28:16PM +0100, Michal Hocko wrote: >>> On Wed 15-11-17 14:13:29, Mel Gorman wrote: >>> [...] >>>> I doubt anyone well. Even the original reporter appeared to pick that >>>> particular value just to trigger the OOM. >>> >>> Then why do we care at all? The trace buffer size can be configured from >>> the userspace if it is not sufficiently large IIRC. >>> >> >> I guess there is the potential that the trace buffer needs to be large >> enough early on in boot but I'm not sure why it would need to be that large >> to be honest. Bottom line, it's fairly trivial to just serialise meminit >> in the event that it's resized from command line. I'm also ok with just >> leaving this is as a "don't set the buffer that large" > > I would be reluctant to touch the code just because of insane kernel > command line option. > > That being said, I will not object or block the patch it just seems > unnecessary for most reasonable setups I can think of. If there is a > legitimate usage of such a large trace buffer then I wouldn't oppose. >
