Red Hat Bugzilla – Bug 1278985
Fedora should be compiled with CONFIG_CMA=y to enable Contiguous Memory Allocator
Last modified: 2016-03-22 18:00:12 EDT
Description of problem:
Both Fedora 23 Workstation and Server do not enable CMA (Contiguous Memory Allocator), which is required for a few new features, such as 1GB hugepage allocation/deallocation at _runtime_: https://lwn.net/Articles/594435/
RHEL 7.1 and later already enabled this, so why not.
This will benefit various big-memory applications and DMA applications that use CMA.
To enable CMA, please add "CONFIG_CMA=y" to .config for kernel compilation.
Version-Release number of selected component (if applicable):
FC23 (Kernel 4.2.5 as of today)
Steps to Reproduce:
1. (to check the current config) grep CONFIG_CMA /boot/config*
Just says: "# CONFIG_CMA is not set"
Has the line: "CONFIG_CMA=y"
Ubuntu enabled it long ago (at least in UB1404) probably for DMA applications. RHEL did it too since 7.1 and onwards.
I'll turn this on in rawhide for x86_64. CMA is mostly stable now but it's a big enough change that turning it on in stable releases really calls for more testing.
Thanks, I'll try rawhide when you push the change.
(In reply to Laura Abbott from comment #1)
> I'll turn this on in rawhide for x86_64. CMA is mostly stable now but it's a
> big enough change that turning it on in stable releases really calls for
> more testing.
Just as a data point we've had it enabled in ARMv7 for some time as it was needed there for some display support.
In at least Fedora 23 in 4.4+