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文章阅读:[转载] Wonderful World of Linux 2.4 (part II)
[版面: Linux 操作系统] [作者:ayanami] , 2000年11月26日17:54:42
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发信人: ayanami (发情的蚊子~甲亢中), 信区: Linux
标  题: [转载] Wonderful World of Linux 2.4 (part II)
发信站: The unknown SPACE (Sun Nov 26 17:54:42 2000), 转信

【 以下文字转载自 ITnews 讨论区 】
【 原文由 ayanami 所发表 】
Linux Internals
Linux 2.2 was a major improvement over Linux 2.0 and the
Linux 1.x series. It supported many new filesystems, a new
system of file caching, and it was much more scalable. (If
you want a list of features new to Linux 2.2, you can read
my article about it.) Linux 2.4builds on these things and
more to be the best darned Linux kernel yet in a variety of
situations.

The Linux kernel is an assortment of modular components and
subsystems including device drivers, protocols, and other
component types. These are glued to the core of the Linux
kernel by APIs, programming interfaces, that provide a
standard method by which the Linux kernel can be expanded.
Most of this document will focus on these components of the
Linux OS as these are the components that seem to do the
most work: drive your disks, read your files, and do all of
the obvious and physical things. Linux 2.4 is however much
more than just these components. These assorted drivers and
APIs all revolve around a common center of the Linux kernel.
This center includes such fundamental features as the
scheduler, the memory manager, the virtual filesystem, and
the resource allocator.

Linux 2.4 is the first release of the Linux kernel which
will include a full-featured resource management subsystem.
Previous incarnations of Linux included some vestiges of
support, but it was considered kludgy and did not provide
the functionality needed for the "Plug and Play" world that
we live in today. Unlike many of the other internal changes,
many users will be able to directly experience this change
as it impacts the way resources are allocated and reported
in the kernel. As part of this change, the PCI card database
deprecated in Linux 2.2 has been un-deprecated so that all
resources can have an associated device name, rather than
just an associated driver.

The new release of the Linux kernel also fixes some problems
with the way the VFS (virtual filesystem) layer and the file
caches were handled. In previous versions of Linux, file
caching was dependent on a dual-buffer system which
simplified some issues, but caused many headaches for kernel
developers who had to make sure that it was not possible for
these buffers to be out of synch. Additionally, the presence
of the redundant buffer increased memory use and slowed down
the system as the kernel would have to do extra work to keep
things in synch. Linux 2.4 solves these problems by moving
to a simpler single-buffer system.

A number of changes in Linux 2.4 can be described
as"enterprise level." That is, they may not be immediately
useful to many desktop users but work to strengthen Linux as
a whole. For the most part, the addition of these features
does not degrade Linux in more "normal"environments. First,
Linux 2.4 can handle many more simultaneous processes by
being more scalable on multiprocessor systems and also by
providing a configurable process limit. Second, the
scheduler has been revised somewhat to be more efficient on
systems with a larger number of concurrent processes. Third,
the revised Linux kernel can now handle an amazing number of
users and groups-- about 4.2 billion. (And that's a lot of
users!) In addition, support for more powerful hardware is
provided in the new kernel which now supports up to 64
gigabytes of RAM on Intel hardware, up to 16 ethernet cards,
10 IDE controllers, multiple IO-APICs,and other pointless
abuses of good hardware. The 2 gigabyte file size
restriction has also been lifted. With these changes and
others, the Linux kernel development team is proving that
Linux can be an option in many new environments.

The way Linux handles shared memory has also been changed in
Linux 2.4 to be more standards compliant. One side effect of
this    set of changes is that Linux 2.4 will require a
special "shared memory" filesystem to be mounted in order
for (POSIX-style) shared memory segments to work. SysV-style
shared memory will continue to work without the additional
filesystem. The mounting of this filesystem should be
handled by the distributions when they become ready for
Linux 2.4.

Another "odd" change included in this new revision of the
Linux kernel involves the VFS layer. In previous versions of
Linux, indeed most every version of UNIX, you can only mount
a filesystem once. Linux 2.4 has decided to turn this on its
ear by allowing any filesystem to be mounted as many times
as desired (with all changes appearing immediately on the
other mount points). This is especially useful for
filesystems like /proc that need to be mounted in an initrd
and then mounted again. Additionally, the infrastructure is
there to eventually allow even odder things: union mounts
which contain files from multiple filesystems together, etc.
In this respect,Linux is either cutting edge or crazy. I'm
betting on the former. :)

Linux 2.4 also includes a much larger assortment of device
drivers and supported hardware than any other Linux revision
and any particular device you care to name has a decent shot
at working under Linux 2.4. (Of course, you should consult
the documentation before you go out and buy any new
hardware, just in case. New hardware especially may not be
supported yet.)

One frequently asked question about Linux 2.4 is how much
memory it will require. Many operating systems seem to
require more and more memory and resources as they mature,
but Linux 2.4 will largely buck that trend by actually
requiring less memory in certain situations. Of course,
Linux 2.4 includes much more functionality than does Linux
2.2and many of these features do take up space so your
mileage may vary. (Remember that most kernel components can
be disabled at compile-time, unlike the bloat of many other
operating systems.)


--
Linux is only free when your time has no value
                                - JWZ

※ 来源:.The unknown SPACE bbs.mit.edu.[FROM: 167.95.252.64.s]
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※ 转载:.The unknown SPACE bbs.mit.edu.[FROM: 64.252.95.167]

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