linux/drivers/usb
Eric Dumazet 5160ee6fc8 [PATCH] shrink dentry struct
Some long time ago, dentry struct was carefully tuned so that on 32 bits
UP, sizeof(struct dentry) was exactly 128, ie a power of 2, and a multiple
of memory cache lines.

Then RCU was added and dentry struct enlarged by two pointers, with nice
results for SMP, but not so good on UP, because breaking the above tuning
(128 + 8 = 136 bytes)

This patch reverts this unwanted side effect, by using an union (d_u),
where d_rcu and d_child are placed so that these two fields can share their
memory needs.

At the time d_free() is called (and d_rcu is really used), d_child is known
to be empty and not touched by the dentry freeing.

Lockless lookups only access d_name, d_parent, d_lock, d_op, d_flags (so
the previous content of d_child is not needed if said dentry was unhashed
but still accessed by a CPU because of RCU constraints)

As dentry cache easily contains millions of entries, a size reduction is
worth the extra complexity of the ugly C union.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: Maneesh Soni <maneesh@in.ibm.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Ian Kent <raven@themaw.net>
Cc: Paul Jackson <pj@sgi.com>
Cc: Al Viro <viro@ftp.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: Neil Brown <neilb@cse.unsw.edu.au>
Cc: James Morris <jmorris@namei.org>
Cc: Stephen Smalley <sds@epoch.ncsc.mil>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-08 20:13:58 -08:00
..
atm [PATCH] USB: small cleanups 2006-01-04 13:48:34 -08:00
class Merge git://git.kernel.org/pub/scm/linux/kernel/git/bunk/trivial 2006-01-04 16:34:57 -08:00
core [PATCH] shrink dentry struct 2006-01-08 20:13:58 -08:00
gadget [PATCH] USB: Use ARRAY_SIZE macro 2006-01-04 13:51:43 -08:00
host [PATCH] fix more missing includes 2006-01-08 20:13:45 -08:00
image [PATCH] USB: remove .owner field from struct usb_driver 2006-01-04 13:48:34 -08:00
input Input: add missing keys from input.h to hid-debug.h 2006-01-05 23:00:26 -05:00
media [PATCH] i2c: Drop i2c_driver.{owner,name}, 5 of 11 2006-01-05 22:16:23 -08:00
misc [PATCH] USB: Remove unneeded kmalloc() return value casts 2006-01-04 13:51:43 -08:00
mon [PATCH] USB: Let usbmon collect less garbage 2006-01-04 13:51:41 -08:00
net [PATCH] USB: zd1201: make sysfs device symlink 2006-01-04 13:51:44 -08:00
serial Merge git://git.kernel.org/pub/scm/linux/kernel/git/bunk/trivial 2006-01-04 16:34:57 -08:00
storage [PATCH] USB Storage: Fix unusual_devs.h order 2006-01-04 13:51:44 -08:00
Kconfig [PATCH] USB: add S3C24XX USB Host driver support 2005-07-29 13:12:53 -07:00
Makefile [PATCH] USB: drivers/usb/storage/libusual 2006-01-04 13:48:31 -08:00
README Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
usb-skeleton.c [PATCH] USB: fix usb-skeleton limit resource usage patch. 2006-01-04 13:51:45 -08:00

To understand all the Linux-USB framework, you'll use these resources:

    * This source code.  This is necessarily an evolving work, and
      includes kerneldoc that should help you get a current overview.
      ("make pdfdocs", and then look at "usb.pdf" for host side and
      "gadget.pdf" for peripheral side.)  Also, Documentation/usb has
      more information.

    * The USB 2.0 specification (from www.usb.org), with supplements
      such as those for USB OTG and the various device classes.
      The USB specification has a good overview chapter, and USB
      peripherals conform to the widely known "Chapter 9".

    * Chip specifications for USB controllers.  Examples include
      host controllers (on PCs, servers, and more); peripheral
      controllers (in devices with Linux firmware, like printers or
      cell phones); and hard-wired peripherals like Ethernet adapters.

    * Specifications for other protocols implemented by USB peripheral
      functions.  Some are vendor-specific; others are vendor-neutral
      but just standardized outside of the www.usb.org team.

Here is a list of what each subdirectory here is, and what is contained in
them.

core/		- This is for the core USB host code, including the
		  usbfs files and the hub class driver ("khubd").

host/		- This is for USB host controller drivers.  This
		  includes UHCI, OHCI, EHCI, and others that might
		  be used with more specialized "embedded" systems.

gadget/		- This is for USB peripheral controller drivers and
		  the various gadget drivers which talk to them.


Individual USB driver directories.  A new driver should be added to the
first subdirectory in the list below that it fits into.

image/		- This is for still image drivers, like scanners or
		  digital cameras.
input/		- This is for any driver that uses the input subsystem,
		  like keyboard, mice, touchscreens, tablets, etc.
media/		- This is for multimedia drivers, like video cameras,
		  radios, and any other drivers that talk to the v4l
		  subsystem.
net/		- This is for network drivers.
serial/		- This is for USB to serial drivers.
storage/	- This is for USB mass-storage drivers.
class/		- This is for all USB device drivers that do not fit
		  into any of the above categories, and work for a range
		  of USB Class specified devices. 
misc/		- This is for all USB device drivers that do not fit
		  into any of the above categories.