Under The Linux 2.6.22 Hood

There's more than better memory management afoot.
The third Linux kernel release of 2007 is now out with memory management and wireless among its improvements.

The 2.6.22 kernel release comes after seven release candidates were put out with the first one issued in May. It includes a long list of update and improvements which Linux founder Linus Torvalds was keen to boast about.

"You want a new firewire stack? We've got it," Torvalds wrote in a mailing list posting. "New wireless networking infrastructure? Check. New infiniband drivers? Digital video drivers? A totally new CPU architecture (blackfin)? Check, check, check."

Linux kernel memory management is expected to get a boost with the new Slub allocator, which will eventually replace the Slab allocator. Slub manages cached objects and is intended to be more space efficient and faster than its predecessor.

"SLAB has overhead at the beginning of each slab. This means that data cannot be naturally aligned at the beginning of a slab block," Linux Kernel developer Christoph Lameter wrote in his original proposal for Slub. "SLUB keeps all meta data in the corresponding page_struct. Objects can be naturally aligned in the slab. For example, a 128 byte object will be aligned at 128 byte boundaries and can fit tightly into a 4k page with no bytes left over. SLAB cannot do this."

The new wireless stack in the Linux 2.6.22 kernel is not the first time kernel developers have tried to improve wireless connectivity in the 2.6.x kernel. In October 2005, for example, the 2.6.14 kernel was released, bringing with it the promise of an improved wireless stack. WiFi vendor Devicescape donated the new 2.6.22 wireless stack to the Linux kernel, which adds 802.11g support and improved quality of service support for VoIP prioritization. (Internetnews.com contacted Devicescape for comment about their Linux efforts but did not receive comment by publication time.)

Firewire support also gets a rewrite in 2.6.22, that, like the Slub update, is intended to be more code efficient.

Flash drives get attention in the new kernel with the UBI (Unsorted Block Images) storage approach, which, according to developers, manages multiple logical volumes on a single flash device.

"UBI provides a flexible partitioning concept, which still allows for wear-levelling across the whole flash device," Linux developer Artem B. Bityutskiy wrote in his kernel commit posting. "In a sense, UBI may be compared to the Logical Volume Manager (LVM). Whereas LVM maps logical sector numbers to physical HDD sector numbers, UBI maps logical eraseblocks to physical eraseblocks."

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