Seems posix_memalign let you choose a customized alignment,but when is that necessary?
malloc has already done the alignment work internally.
UPDATE
The exact reason I ask this is because I see nginx does this,ngx_memalign(NGX_POOL_ALIGNMENT, size, log);,here NGX_POOL_ALIGNMENT is defined as 16, nginxs.googlecode.com/svn-history/trunk/src/core/ngx_palloc.c