Linux 3.2 [ released] on 4 Jan 2012

Summary: This release includes support for ext4 block sizes bigger than 4KB and up to 1MB, which improve performance with big files; btrfs has been updated with faster scrubbing, automatic backup of critical filesystem metadata and tools for manual inspection of the filesystems; the process scheduler has added support to set upper limits of CPU time; the desktop reponsiveness in presence of heavy writes has been improved, TCP has been updated to include an algorithm which speeds up the recovery of the connection after lost packets; the profiling tool "perf top" has added support for live inspection of tasks and libraries and see the annotated assembly code; the Device Mapper has added support for 'thin provisioning' of storage, and a new architeture has been added: the Hexagon DSP processor from Qualcomm. Other drivers and small improvements and fixes are also available in this release.


1. Prominent features in Linux 3.2

1.1. ext4: Support for bigger block sizes

Recommended LWN article: [ Improving ext4: bigalloc, inline data, and metadata checksums]

The maximum size of a filesystem block in ext4 has always been 4 KB in x86 systems. But the storage capacity of modern hard disks is growing fast, and with the size of hard disks, the overhead of using such small size as block size increases. Small block sizes benefit users who have many small files, because the space will be used more efficiently, but people who uses large files would benefit of larger block sizes.

ext4 supports now block sizes of up to 1MB of size, which decreases considerably [ the time spent doing block allocations], and there is smaller fragmentation. These new block sizes must be set at creation time, using the mkfs -C option (requires e2fsprogs 1.42). This feature is not backwards compatible with older kernels. Code: [ (commit 1], [ 2], [ 3], [ 4], [ 5], [ 6], [ 7], [ 8], [ 9], [ 10], [ 11], [ 12], [ 13], [ 14], [ 15], [ 16], [ 17)]

1.2. Btrfs: Faster scrubbing, automatic backup of tree roots, detailed corruption messages, manual inspection of metadata

Recommended LWN article: [ A btrfs update at LinuxCon Europe]

Scrub read-ahead

Scrubbing -the process of checking all the checksums of the filesystem- uses read-ahead to improve the performance. The average disk bandwith utilisation on a test volume was raised from 70% to 90%. On another volume, the time for a test run went down from 89 seconds to 43 seconds. Code: [ (commit 1], [ 2], [ 3], [ 4)]

Log of past tree roots
Btrfs will store in the filesystem superblock information about most of the tree roots in the last four commits. A "-o recovery" mount option has been used to allow a user to use the root history log when the filesystem is not able to read the tree

KernelNewbies: Linux_3.2 (last edited 2012-07-22 14:03:05 by diegocalleja)