Is there a limit on memory allocated using huge pages?

Question

I am allocating memory using "huge pages(1MB size)" and using mmap. After allocating 4 GB of memory ,mmap returns fail.

mmap(NULL, memsize, PROT_READ | PROT_WRITE,MAP_PRIVATE | MAP_ANONYMOUS |MAP_POPULATE | MAP_HUGETLB, -1, 0);

here memsize = 1GB

I am calling above statement in a loop. Upto 4 iterations it is fine. In 5th iteration mmap is failed.

mmap(NULL, memsize, PROT_READ | PROT_WRITE,MAP_PRIVATE | MAP_ANONYMOUS |MAP_POPULATE , -1, 0);

Above statement (without hugepages) works perfectly for any number of iterations. Am I missing any information related to hugepages? I tried "MAP_NORESERVE" flag also as mentioned in mmap fail after 4GB.

Any sort of information will be greatly appreciated. Thank you.

How much is available on your system? You can list it using `cat /proc/meminfo | grep HugePages` . Additional reading: https://www.kernel.org/doc/Documentation/vm/hugetlbpage.txt — Klas Lindbäck, May 16 '16 at 13:47
@KevinDTimm : i checked return value (MAP_FAILED) then only i concluded mmap failed. — ANTHONY, May 16 '16 at 16:11
@KlasLindbäck Thanks. That did help. Do you have any CLEAR idea about Rsvd and Surp ,how and when they are used? — ANTHONY, May 16 '16 at 16:41

score 2 · Accepted Answer · edited May 17 '16 at 07:25

Change the allocated "number of huge pages" in file

 /proc/sys/vm/nr_hugepages

according to the amount of memory you want to allocate. Earlier it says:

>cat /proc/meminfo | grep HugePages 
 HugePages_Total = 2500

4GB => it has 2048*2Mb= 4Gb

2048 huge pages already consumed.

one more GB of memory need (1GB/2MB= 512) 512 more huge pages. But 2500 - 2048 =452 only left. But you need 512. Thats the problem why mmap failed. If you edit the above mentioned file(/proc/sys/vm/nr_hugepages) contents to 2560, it allows 5GB. Change it according to the amount of memory you need. Thanks to @ Klas Lindbäck. I referred back the link, small research exposed the working

Is there a limit on memory allocated using huge pages?

1 Answers1