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10. Kernel
Kdump Auto Enablement
Kdump is now enabled by default on systems with large amounts of memory. Specifically, kdump is enabled by default on:
systems with more than 4GB of memory on architectures with a 4KB page size (i.e. x86 or x86_64), or
systems with more than 8GB of memory on architectures with larger than a 4KB page size (i.e PPC64).
On systems with less than the above memory configurations, kdump is not auto enabled. Refer to /usr/share/doc/kexec-tools-2.0.0/kexec-kdump-howto.txt for instructions on enabling kdump on these systems.
crashkernel parameter syntax
Please note that in future versions of Red Hat Enterprise Linux 6 (i.e. Red Hat Enterprise Linux 6.1 and later) the auto value setting of the crashkernel= parameter (i.e. crashkernel=auto) will be deprecated.
Barrier Implementation in the Kernel
The barrier implementation in the Red Hat Enterprise Linux 6 kernel works by completely draining the I/O scheduler's queue, then issuing a preflush, a barrier, and finally a postflush request. However, since the supported file systems in Red Hat Enterprise Linux 6 all implement their own ordering guarantees, the block layer need only provide a mechanism to ensure that a barrier request is ordered with respect to other I/O already in the disk cache. This mechanism avoids I/O stalls experienced by queue draining. The block layer will be updated in future kernels to provide this more efficient mechanism of ensuring ordering.
Workloads that include heavy fsync or metadata activity will see an overall improvement in disk performance. Users taking advantage of the proportional weight I/O controller will also see a boost in performance. In preparation for the block layer updates, third party file system developers need to ensure that data ordering surrounding journal commits are handled within the file system itself, since the block layer will no longer provide this functionality.
These future block layer improvements will change some kernel interfaces such that symbols which are not on the kABI whitelist shall be modified. This may result in the need to recompile third party file system or storage drivers.
Systemtap Tracepoints
The following 3 virtual memory tracepoints are deprecated in Red Hat Enterprise Linux 6
trace_mm_background_writeout(unsigned long written)
trace_mm_olddata_writeout(unsigned long written)
trace_mm_balancedirty_writeout(unsigned long written)
10.1. Technology Previews
Remote Audit Logging
The audit package contains the user space utilities for storing and searching the audit records generated by the audit subsystem in the Linux 2.6 kernel. Within the audispd-plugins subpackage is a utility that allows for the transmission of audit events to a remote aggregating machine. This remote audit logging application, audisp-remote, is considered a Technology Preview in Red Hat Enterprise Linux 6.
Linux (NameSpace) Container [LXC]
Linux (NameSpace) Containers [LXC] is a Technology Preview feature in Red Hat Enterprise Linux 6 Beta that provides isolation of resources assigned to one or more processes. A process is assigned a separate user permission, networking, filesystem name space from its parent.
Error Detection And Correction (EDAC) driver interface
The Error Detection And Correction (EDAC) driver interface for processors based on the Intel microarchitecture codename Nehalem is considered a Technology Preview in this pre-release version of Red Hat Enterprise Linux 6.
