User`s guide

Memory Management

• Add persistent function tracing. The kernel can save the function call chain log to a persistent RAM

buffer, which can be decoded and dumped after a reboot. You can use the log to determine the function

that was called immediately prior to a reset or panic. (3.6)

tmpfs

• Increase the file size limit for tmpfs. (3.1)

• Support fallocate() FALLOC_FL_PUNCH_HOLE and preallocation. (3.5)

XFS

• Improve performance of the inode cache. (3.1)

• Improve scalability of per-file-system quotas. (3.4)

• Implement support for SEEK_DATA and SEEK_HOLE. (3.5)

• Make the inode32 and inode64 mount options work with remounts. (3.7)

• Make inode64 the default allocation mode. (3.7)

• Add the XFS_IOC_FREE_EOFBLOCKS ioctl() to enable EOFBLOCKS scanning. (3.8)

A.8 Memory Management

• Add memory.vmscan_stat memory control group that displays numbers of scanned, rotated, and

freed pages, and elapsed times for direct reclaim and soft reclaim. (3.1)

• Extend the memory hotplug API to allow memory hotplug in virtual machines. Also required for the Xen

balloon driver. (3.1)

• Fix significant stalls in the page allocator when copying large amounts of data on NUMA machines. (3.1)

• Add slub_debug method to the slub slab allocator to check if memory is not freed and help diagnose

memory usage. (3.1)

• Reduce CPU overhead of slub_debug. (3.1)

• The cross memory attach feature adds the system calls process_vm_readv and

process_vm_writev(), which allow data to be transferred between the address spaces of the two

processes without passing through kernel space. (3.2)

• Add a block plug for page reclaim to vmscan that reduces CPU overhead by reducing lock contention

and merging requests. (3.2)

• Implement per-CPU cache in slub for partial pages. (3.2)

• Restrict access to slab files under procfs and sysfs, hiding slabinfo and /sys/kernel/slab/*.

(3.2)

• Add the slab_max_order kernel parameter that determines the maximum allowed order for slabs. High

settings can cause OOMs due to memory fragmentation. The default value is 1 for systems with more

than 32 MB of RAM. Otherwise, the default value is 0. (3.3)

• To increase the probability of detecting memory corruption, change the buddy allocator to retain more

free, protected pages and to interlace free, protected pages and allocated pages. (3.3)