User`s guide

Core Kernel Functionality

• The prctl() PR_GET_CHILD_SUBREAPER and PR_SET_CHILD_SUBREAPER options implement

simple process supervision of orphaned processes. (3.4)

• Thread stacks are now marked correctly for proc/pid/maps under procfs. (3.4)

• Restore the sysctl setting kernel.pty.max as the global limit of pseudo terminals (by default, 4096).

(3.4)

• Add abilities to turn the reboot notifier on or off, and to enter the debugger and stop kernel execution

before rebooting. (3.4)

• To improve performance, VFS now uses unsigned long accesses for dcache name comparison and

hashing. (3.4)

• /proc/pid/task/tid/children entries provide information about task children and can be useful

for process checkpoint and restore operations. (3.5)

• /proc/pid/pagemap now reports whether file pages are shared-anon or file-page. (3.5)

• The skew_tick boot option mitigates xtime_lock contention on larger systems or read-copy-update

(RCU) lock contention on all systems when CONFIG_MAXSMP is set. This option increases power

consumption and should only be enabled if the system runs jitter-sensitive workloads (typically, HPC or

RT). (3.5)

• Inode stat information is moved closer together to increase the likelihood of cache hits. (3.5)

• The fallocate() file-system operation allows preallocation space for a file. (3.5)

• Stale power-aware scheduling remnants and dysfunctional knobs have been removed from the process

scheduler. (3.5)

• The EPOLLWAKEUP flag prevents system suspension while epoll events are ready. (3.5)

• ramoops uses the pstore interface instead of /dev/mem. (3.5)

• Add ECC support to pstore/ram. (3.5)

• make tools is now integrated with the kernel build system. (3.5)

• The kernel parameter RCU_FANOUT_LEAF can be used to control leaf-level fanout for RCU locking to

reduce cache-miss initialization latencies on large systems. (3.5)

• RCU locking now implements a direct algorithmic sleepable RCU (SRCU) implementation to prevent OS

jitter and performance degredation. (3.5)

• Add rbtree node caching support to IPC mqueue for the case where the queue is empty, improve

performance of send/recv, and update maximums for the mqueue subsystem. (3.5)

• Add symbolic and hard link restrictions to VFS to address security issues. (3.6)

• Improvements to the IOMMU group implementation. (3.6)

• Remove the non-working x86 power estimation feature from the process scheduler. (3.6)

• Add hysteresis attributes (used by most thermal sensors) on a per-trip-point basis to the thermal

framework. (3.6)

• Add support for states that affect multiple CPUs. This is potentially useful in implementations where

CPUs leverage a shared, coupled power state. (3.6)