Red Hat Bugzilla – Bug 103229
LTC4129-CONFIG_X86_4G is on by default
Last modified: 2007-11-30 17:06:57 EST
The following has be reported by IBM LTC:
CONFIG_X86_4G is on by default
Apparently, CONFIG_X86_4G is on by default in all kernels in RHEL 3.0. This
breaks GPFS in a very bad way, because GPFS has userspace and kernel components
that communicate via a shared region in kernel memory area, and this options
makes kernel space inaccessible from userspace. There's no workaround. This
option is only needed for big-memory machines, and imposes a severe performance
penalty, and it's not clear why it's on by default on all kernels.Glen/Greg -
please submit this to Red Hat. Thanks.
*** This bug has been marked as a duplicate of 78616 ***
also your statement is incorrect.
It shows that your binary only filesystem is incorrectly coded. Several other
(GPL) modules DO have shared kernel/userspace memory and work JUST FINE with
4G/4G split, but they are coded properly
------- Additional Comment #5 From Yuri L. Volobuev 2003-08-27 18:57 -------
In response to RH bugzilla comment:
Just for the record, the portion of GPFS code that sets up the shared memory
region is open-sourced (BSD license), so please stop bringing in "binary only"
as an issue. Not every GPFS problem is automatically caused by its
non-opensourcenes. The real issue is the method for setting up a shared memory
region. GPFS does it in an unusual way, for historical reasons. Whether this
way is "incorrect" can be debated. It's worked so far.
Aside from the issue of GPFS breaking, one should be concerned about other
implications of this option, namely the stiff performance penalty of frequent
TLB flushes. Given that the option is only applicable on machines with more
than 1GB of RAM, and the option help blurb itself states that machines with less
than 4GB of RAM will rarely see any benefit from this option. So why enable it
by default in all kernels? Wouldn't it make more sense to only enable it in a
Config was on in B1 for broad testing of our 4G/4G split.
It is now only on in the hugemem kernel.
------ Additional Comments From email@example.com 2003-28-08 15:06 -------
Yuri - Please verify that the config_x86_4G option is not on by default
in beta2. Please re-open this bug report if it is still on. Thanks.
------ Additional Comments From firstname.lastname@example.org 2003-29-08 19:33 -------
Verified that CONFIG_X86_4G is only on in hugemem kernel in beta2. Issue
Changed to 'CLOSED' state since 'RESOLVED' has been deprecated.