昨天@淘寶雕樑 同學推薦了無鎖的記憶體分配器，上網站粗粗的瞭解了下，這家叫Lockless的公司主要有2個產品：
Lockless MPI 和 Lockless Memory Allocator， 我對記憶體分配器比較感興趣，它對高效能伺服器的影響還是非常大的,特別是mysql這樣的伺服器，看它的文件對效能的提升好像比較明顯。

我們重點來了解下 Lockless Memory Allocator:

The Lockless Memory Allocator is downloadable under the GPL 3.0 License.

官網強調的特性：

Multithread Optimized
The Lockless memory allocator uses lock-free techniques to minimize latency and memory contention. This provides optimal scalability as the number of threads in your application increases. Per-thread data is used to reduce bus communication overhead. This results in thread-local allocations and frees not requiring any synchronization overhead in most cases.

官網做的和主流的幾種分配器的效能比較：

詳細的bechmark見這裡，看上去讓人挺印象深刻的。

程式碼在這裡下載 http://locklessinc.com/downloads/， 支援32位和64位的Linux, 安裝文件在這裡

我們來嚐鮮實驗下：

$  wget http://locklessinc.com/downloads/lockless_allocator_src.tgz
$ tar xzf lockless_allocator_src.tgz 
$ cd lockless_allocator
$ gcc -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk --disable-dssi --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre --enable-libgcj-multifile --enable-java-maintainer-mode --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib --with-ppl --with-cloog --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 4.4.5 20110214 (Red Hat 4.4.5-6) (GCC) 

$ make
/bin/sh -ec 'gcc -MM  ll_alloc.c | sed -n "H;$ {g;
 
[email protected]*:\(.*\)@ll_alloc.c := \$\(wildcard\1\)\nll_alloc.o ll_alloc.c.d: $\(ll_alloc.c\)@;p}" > ll_alloc.c.d'
cc ll_alloc.c -fomit-frame-pointer -Wcast-qual -Wmissing-format-attribute -Wlogical-op -Wstrict-aliasing -Wsign-compare -Wdeclaration-after-statement -Wnested-externs -Wdisabled-optimization -Winline -Wundef -Wimplicit -Wunused -Wfloat-equal -Winit-self -Wformat=2 -Wswitch -Wsequence-point -Wparentheses -Wimplicit -Wchar-subscripts -Wredundant-decls -Wstrict-prototypes -Wbad-function-cast -Wpointer-arith -Wwrite-strings -Wno-long-long -Wmissing-declarations -Wmissing-prototypes -Wextra -Wall -pedantic -ggdb3 -std=gnu99 -O3  -fPIC -pthread -c -o libllalloc.o 
strip -g libllalloc.o
ar rcs libllalloc.a libllalloc.o
ranlib libllalloc.a
cc ll_alloc.c -fomit-frame-pointer -Wcast-qual -Wmissing-format-attribute -Wlogical-op -Wstrict-aliasing -Wsign-compare -Wdeclaration-after-statement -Wnested-externs -Wdisabled-optimization -Winline -Wundef -Wimplicit -Wunused -Wfloat-equal -Winit-self -Wformat=2 -Wswitch -Wsequence-point -Wparentheses -Wimplicit -Wchar-subscripts -Wredundant-decls -Wstrict-prototypes -Wbad-function-cast -Wpointer-arith -Wwrite-strings -Wno-long-long -Wmissing-declarations -Wmissing-prototypes -Wextra -Wall -pedantic -ggdb3 -std=gnu99 -O3  -shared -fpic -Wl,-soname,libllalloc.so.1.3 -Wl,-z,interpose -o libllalloc.so.1.3 
strip libllalloc.so.1.3

$ ls libllalloc.*
libllalloc.a  libllalloc.o  libllalloc.so.1.3

$ LD_PRELOAD=./libllalloc.so.1.3  erl
Erlang R14B04 (erts-5.8.5)  [64-bit] [smp:16:16] [rq:16] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.8.5  (abort with ^G)
1> 

#另外一個終端確認libllalloc.so.1.3在使用
$ lsof  -c beam.smp
COMMAND   PID           USER   FD      TYPE DEVICE     SIZE    NODE NAME
beam.smp 8458          chuba  txt       REG    8,5  2344032 3775338 /usr/local/lib/erlang/erts-5.8.5/bin/beam.smp
...
beam.smp 8458          chuba  mem       REG    8,6    40384  195304 /home/chuba/lockless_allocator/libllalloc.so.1.3
...

這裡面有個問題： 編譯的時候需要的gcc版本比較高，gcc version 4.1.2 20080704 (Red Hat 4.1.2-46)編譯不過。
之前tcmalloc就沒通過erl的使用，因為erlang內部的指標的後4位被用了，如果分配器不遵守16位元組對齊，就會出問題。

看了程式碼實現的也很簡單，程式碼質量也一般，不知道具體的效能如何，後續找個案例benchmark下！
未完待續！

祝玩得開心！

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