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On the box we have 38 GBs of memory. After I have set the number of huge pages (2048k) to 17290, I've found out that nearly all of the memory was used. But I didn't run any process. How could it be? Which number of huge pages should I set?
user710818
Posted 2014-08-04T12:23:44.383
Reputation: 340
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You've reserved almost all your memory for huge tlb pages. That leaves almost no memory to store actual data. The recommend size is about 1/1,000th of what you've set it to.
David Schwartz
Posted 2014-08-04T12:23:44.383
Reputation: 58 310
0
This question is old, but I think the other answer is wrong. Depending on how huge pages have been allocated exactly, if done properly at that time using
echo 17290 > /proc/sys/vm/nr_hugepages
or something like that, what has been seen was intended behaviour and is as documented. It is absolutely OK to reserve the number of huge pages one thinks is needed for ones workload and that almost all free memory is gone in the described scenario is as expected as well:
Pages that are used as huge pages are reserved inside the kernel and cannot be used for other purposes. Huge pages cannot be swapped out under memory pressure.
https://www.kernel.org/doc/Documentation/vm/hugetlbpage.txt
Others do exactly the same:
Set the vm.nr_hugepages kernel parameter to a suitable value. In this case, we decided to use 12GB and set the parameter to 6144 (6144*2M=12GB). You can run: echo 6144 > /proc/sys/vm/nr_hugepages
https://blog.pythian.com/performance-tuning-hugepages-in-linux/
Thorsten Schöning
Posted 2014-08-04T12:23:44.383
Reputation: 523
My java application that uses near 35G and uses LargePages(-XX:+UseLargePages). So I guess that total space for huge pages should be near 35G. – user710818 – 2014-08-04T12:39:46.220
@user710818 The "number of huge pages" that you set has nothing to do with the number of huge pages the application uses. It has to do with the number of huge page TLBs used by the OS. – David Schwartz – 2014-08-04T12:40:49.203
So it should be 17 pages only? – user710818 – 2014-08-04T12:58:13.980
That's the recommendation. – David Schwartz – 2014-08-04T16:51:06.057
Downvote, because I think this answer is wrong and what has been seen is as expected: https://superuser.com/a/1327823/308859
– Thorsten Schöning – 2018-06-01T15:44:28.460