Kernel Log: Coming in 2.6.38 (Part 2) � File system

“Linux 2.6.38 contains patches to improve the scalability of VFS
that has been the topic of much discussion for the past six months
and that Torvalds himself was waiting for. Ext3 and XFS now support
batched discard, which is interesting for SSDs, while Btrfs and
SquashFS support additional compression technologies.

“On Wednesday, Linus Torvalds released the fifth pre-release of
kernel version 2.6.38 saying that some regressions have been fixed
and other changes are “pretty spread out and small”. The Kernel Log
therefore takes the opportunity to continue the overview of the
major changes in Linux 2.6.38 with the second part of the
mini-series “Coming in 2.6.38”. Part one discussed the main changes
pertaining to graphics drivers, and in the next few weeks we will
be discussing network support, storage hardware, drivers, and code
for architecture and infrastructure.

“Optimising VFS

“Some of the optimisations of VFS (Virtual File System), which
offers basic functions for all file systems, in 2.6.38 were
especially important for Torvalds, who could not hide his
excitement in a detailed description in an email on the first
pre-release version of 2.6.38 (see 1, 2, 3, 4, 5, 6, 7). The basis
for all file systems, VFS uses finer locking with RCU (read copy
update) thanks to these changes developed under such names as
“RCU-based name lookup”, in order to considerably accelerate a
number of operations in the resolution of file names. Large servers
with a number of processor cores will not be the only ones to
benefit; off-the-shelf systems also will. In his release email,
Torvalds says the performance improvements range from 30 to 50 per
cent in certain tests of file and name resolution.”

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