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third_party/git/compat/nedmalloc/Readme.txt

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+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. Further 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