compat/nedmalloc/Readme.txt - jrn/git - Git at Google

 nedalloc v1.05 15th June 2008:
 -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

 by Niall Douglas (http://www.nedprod.com/programs/portable/nedmalloc/)

 Enclosed is nedalloc, an alternative malloc implementation for multiple
 threads without lock contention based on dlmalloc v2.8.4. It is more
 or less a newer implementation of ptmalloc2, the standard allocator in
 Linux (which is based on dlmalloc v2.7.0) but also contains a per-thread
 cache for maximum CPU scalability.

 It is licensed under the Boost Software License which basically means
 you can do anything you like with it. This does not apply to the malloc.c.h
 file which remains copyright to others.

 It has been tested on win32 (x86), win64 (x64), Linux (x64), FreeBSD (x64)
 and Apple MacOS X (x86). It works very well on all of these and is very
 significantly faster than the system allocator on all of these platforms.

 By literally dropping in this allocator as a replacement for your system
 allocator, you can see real world improvements of up to three times in normal
 code!

 To use:
 -=-=-=-
 Drop in nedmalloc.h, nedmalloc.c and malloc.c.h into your project.
 Configure using the instructions in nedmalloc.h. Run and enjoy.

 To test, compile test.c. It will run a comparison between your system
 allocator and nedalloc and tell you how much faster nedalloc is. It also
 serves as an example of usage.

 Notes:
 -=-=-=
 If you want the very latest version of this allocator, get it from the
 TnFOX SVN repository at svn://svn.berlios.de/viewcvs/tnfox/trunk/src/nedmalloc

 Because of how nedalloc allocates an mspace per thread, it can cause
 severe bloating of memory usage under certain allocation patterns.
 You can substantially reduce this wastage by setting MAXTHREADSINPOOL
 or the threads parameter to nedcreatepool() to a fraction of the number of
 threads which would normally be in a pool at once. This will reduce
 bloating at the cost of an increase in lock contention. If allocated size
 is less than THREADCACHEMAX, locking is avoided 90-99% of the time and
 if most of your allocations are below this value, you can safely set
 MAXTHREADSINPOOL to one.

 You will suffer memory leakage unless you call neddisablethreadcache()
 per pool for every thread which exits. This is because nedalloc cannot
 portably know when a thread exits and thus when its thread cache can
 be returned for use by other code. Don't forget pool zero, the system pool.

 For C++ type allocation patterns (where the same sizes of memory are
 regularly allocated and deallocated as objects are created and destroyed),
 the threadcache always benefits performance. If however your allocation
 patterns are different, searching the threadcache may significantly slow
 down your code - as a rule of thumb, if cache utilisation is below 80%
 (see the source for neddisablethreadcache() for how to enable debug
 printing in release mode) then you should disable the thread cache for
 that thread. You can compile out the threadcache code by setting
 THREADCACHEMAX to zero.

 Speed comparisons:
 -=-=-=-=-=-=-=-=-=
 See Benchmarks.xls for details.

 The enclosed test.c can do two things: it can be a torture test or a speed
 test. The speed test is designed to be a representative synthetic
 memory allocator test. It works by randomly mixing allocations with frees
 with half of the allocation sizes being a two power multiple less than
 512 bytes (to mimic C++ stack instantiated objects) and the other half
 being a simple random value less than 16Kb.

 The real world code results are from Tn's TestIO benchmark. This is a
 heavily multithreaded and memory intensive benchmark with a lot of branching
 and other stuff modern processors don't like so much. As you'll note, the
 test doesn't show the benefits of the threadcache mostly due to the saturation
 of the memory bus being the limiting factor.

 ChangeLog:
 -=-=-=-=-=
 v1.05 15th June 2008:
  * { 1042 } Added error check for TLSSET() and TLSFREE() macros. Thanks to
 Markus Elfring for reporting this.
  * { 1043 } Fixed a segfault when freeing memory allocated using
 nedindependent_comalloc(). Thanks to Pavel Vozenilek for reporting this.

 v1.04 14th July 2007:
  * Fixed a bug with the new optimised implementation that failed to lock
 on a realloc under certain conditions.
  * Fixed lack of thread synchronisation in InitPool() causing pool corruption
  * Fixed a memory leak of thread cache contents on disabling. Thanks to Earl
 Chew for reporting this.
  * Added a sanity check for freed blocks being valid.
  * Reworked test.c into being a torture test.
  * Fixed GCC assembler optimisation misspecification

 v1.04alpha_svn915 7th October 2006:
  * Fixed failure to unlock thread cache list if allocating a new list failed.
 Thanks to Dmitry Chichkov for reporting this. Futher thanks to Aleksey Sanin.
  * Fixed realloc(0, <size>) segfaulting. Thanks to Dmitry Chichkov for
 reporting this.
  * Made config defines #ifndef so they can be overridden by the build system.
 Thanks to Aleksey Sanin for suggesting this.
  * Fixed deadlock in nedprealloc() due to unnecessary locking of preferred
 thread mspace when mspace_realloc() always uses the original block's mspace
 anyway. Thanks to Aleksey Sanin for reporting this.
  * Made some speed improvements by hacking mspace_malloc() to no longer lock
 its mspace, thus allowing the recursive mutex implementation to be removed
 with an associated speed increase. Thanks to Aleksey Sanin for suggesting this.
  * Fixed a bug where allocating mspaces overran its max limit. Thanks to
 Aleksey Sanin for reporting this.

 v1.03 10th July 2006:
  * Fixed memory corruption bug in threadcache code which only appeared with >4
 threads and in heavy use of the threadcache.

 v1.02 15th May 2006:
  * Integrated dlmalloc v2.8.4, fixing the win32 memory release problem and
 improving performance still further. Speed is now up to twice the speed of v1.01
 (average is 67% faster).
  * Fixed win32 critical section implementation. Thanks to Pavel Kuznetsov
 for reporting this.
  * Wasn't locking mspace if all mspaces were locked. Thanks to Pavel Kuznetsov
 for reporting this.
  * Added Apple Mac OS X support.

 v1.01 24th February 2006:
  * Fixed multiprocessor scaling problems by removing sources of cache sloshing
  * Earl Chew <earl_chew <at> agilent <dot> com> sent patches for the following:
    1. size2binidx() wasn't working for default code path (non x86)
    2. Fixed failure to release mspace lock under certain circumstances which
       caused a deadlock

 v1.00 1st January 2006:
  * First release
	nedalloc v1.05 15th June 2008:
	-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

	by Niall Douglas (http://www.nedprod.com/programs/portable/nedmalloc/)

	Enclosed is nedalloc, an alternative malloc implementation for multiple
	threads without lock contention based on dlmalloc v2.8.4. It is more
	or less a newer implementation of ptmalloc2, the standard allocator in
	Linux (which is based on dlmalloc v2.7.0) but also contains a per-thread
	cache for maximum CPU scalability.

	It is licensed under the Boost Software License which basically means
	you can do anything you like with it. This does not apply to the malloc.c.h
	file which remains copyright to others.

	It has been tested on win32 (x86), win64 (x64), Linux (x64), FreeBSD (x64)
	and Apple MacOS X (x86). It works very well on all of these and is very
	significantly faster than the system allocator on all of these platforms.

	By literally dropping in this allocator as a replacement for your system
	allocator, you can see real world improvements of up to three times in normal
	code!

	To use:
	-=-=-=-
	Drop in nedmalloc.h, nedmalloc.c and malloc.c.h into your project.
	Configure using the instructions in nedmalloc.h. Run and enjoy.

	To test, compile test.c. It will run a comparison between your system
	allocator and nedalloc and tell you how much faster nedalloc is. It also
	serves as an example of usage.

	Notes:
	-=-=-=
	If you want the very latest version of this allocator, get it from the
	TnFOX SVN repository at svn://svn.berlios.de/viewcvs/tnfox/trunk/src/nedmalloc

	Because of how nedalloc allocates an mspace per thread, it can cause
	severe bloating of memory usage under certain allocation patterns.
	You can substantially reduce this wastage by setting MAXTHREADSINPOOL
	or the threads parameter to nedcreatepool() to a fraction of the number of
	threads which would normally be in a pool at once. This will reduce
	bloating at the cost of an increase in lock contention. If allocated size
	is less than THREADCACHEMAX, locking is avoided 90-99% of the time and
	if most of your allocations are below this value, you can safely set
	MAXTHREADSINPOOL to one.

	You will suffer memory leakage unless you call neddisablethreadcache()
	per pool for every thread which exits. This is because nedalloc cannot
	portably know when a thread exits and thus when its thread cache can
	be returned for use by other code. Don't forget pool zero, the system pool.

	For C++ type allocation patterns (where the same sizes of memory are
	regularly allocated and deallocated as objects are created and destroyed),
	the threadcache always benefits performance. If however your allocation
	patterns are different, searching the threadcache may significantly slow
	down your code - as a rule of thumb, if cache utilisation is below 80%
	(see the source for neddisablethreadcache() for how to enable debug
	printing in release mode) then you should disable the thread cache for
	that thread. You can compile out the threadcache code by setting
	THREADCACHEMAX to zero.

	Speed comparisons:
	-=-=-=-=-=-=-=-=-=
	See Benchmarks.xls for details.

	The enclosed test.c can do two things: it can be a torture test or a speed
	test. The speed test is designed to be a representative synthetic
	memory allocator test. It works by randomly mixing allocations with frees
	with half of the allocation sizes being a two power multiple less than
	512 bytes (to mimic C++ stack instantiated objects) and the other half
	being a simple random value less than 16Kb.

	The real world code results are from Tn's TestIO benchmark. This is a
	heavily multithreaded and memory intensive benchmark with a lot of branching
	and other stuff modern processors don't like so much. As you'll note, the
	test doesn't show the benefits of the threadcache mostly due to the saturation
	of the memory bus being the limiting factor.

	ChangeLog:
	-=-=-=-=-=
	v1.05 15th June 2008:
	* { 1042 } Added error check for TLSSET() and TLSFREE() macros. Thanks to
	Markus Elfring for reporting this.
	* { 1043 } Fixed a segfault when freeing memory allocated using
	nedindependent_comalloc(). Thanks to Pavel Vozenilek for reporting this.

	v1.04 14th July 2007:
	* Fixed a bug with the new optimised implementation that failed to lock
	on a realloc under certain conditions.
	* Fixed lack of thread synchronisation in InitPool() causing pool corruption
	* Fixed a memory leak of thread cache contents on disabling. Thanks to Earl
	Chew for reporting this.
	* Added a sanity check for freed blocks being valid.
	* Reworked test.c into being a torture test.
	* Fixed GCC assembler optimisation misspecification

	v1.04alpha_svn915 7th October 2006:
	* Fixed failure to unlock thread cache list if allocating a new list failed.
	Thanks to Dmitry Chichkov for reporting this. Futher thanks to Aleksey Sanin.
	* Fixed realloc(0, <size>) segfaulting. Thanks to Dmitry Chichkov for
	reporting this.
	* Made config defines #ifndef so they can be overridden by the build system.
	Thanks to Aleksey Sanin for suggesting this.
	* Fixed deadlock in nedprealloc() due to unnecessary locking of preferred
	thread mspace when mspace_realloc() always uses the original block's mspace
	anyway. Thanks to Aleksey Sanin for reporting this.
	* Made some speed improvements by hacking mspace_malloc() to no longer lock
	its mspace, thus allowing the recursive mutex implementation to be removed
	with an associated speed increase. Thanks to Aleksey Sanin for suggesting this.
	* Fixed a bug where allocating mspaces overran its max limit. Thanks to
	Aleksey Sanin for reporting this.

	v1.03 10th July 2006:
	* Fixed memory corruption bug in threadcache code which only appeared with >4
	threads and in heavy use of the threadcache.

	v1.02 15th May 2006:
	* Integrated dlmalloc v2.8.4, fixing the win32 memory release problem and
	improving performance still further. Speed is now up to twice the speed of v1.01
	(average is 67% faster).
	* Fixed win32 critical section implementation. Thanks to Pavel Kuznetsov
	for reporting this.
	* Wasn't locking mspace if all mspaces were locked. Thanks to Pavel Kuznetsov
	for reporting this.
	* Added Apple Mac OS X support.

	v1.01 24th February 2006:
	* Fixed multiprocessor scaling problems by removing sources of cache sloshing
	* Earl Chew <earl_chew <at> agilent <dot> com> sent patches for the following:
	1. size2binidx() wasn't working for default code path (non x86)
	2. Fixed failure to release mspace lock under certain circumstances which
	caused a deadlock

	v1.00 1st January 2006:
	* First release