The reordering that GCC may do is unrelated to the reordering an (x86) CPU may do. Let’s start off with compiler reordering. The C language rules are such that GCC is forbidden from reordering volatile loads and store memory accesses with respect to each other, or deleting them, when a sequence point occurs between them … Read more
Heap and memory management is a facility provided by your C library (likely glibc). It maintains the heap and returns chunks of memory to you every time you do a malloc(). It doesn’t know heap size limit: every time you request more memory than what is available on the heap, it just goes and asks … Read more
The usual rule of thumb (straight from Intels and AMD’s optimization manuals) is that every data type should be aligned by its own size. An int32 should be aligned on a 32-bit boundary, an int64 on a 64-bit boundary, and so on. A char will fit just fine anywhere. Another rule of thumb is, of … Read more
There are lots of ways in which malloc/free can store the size of the memory area. For example, it might be stored just before the area returned by malloc. Or it might be stored in a lookup table elsewhere. Or it might be stored implicitly: some areas might be reserved for specific sizes of allocations. … Read more
If you want the memory of the entire running process and not on a per thread basis, how about: // get the current process Process currentProcess = System.Diagnostics.Process.GetCurrentProcess(); // get the physical mem usage long totalBytesOfMemoryUsed = currentProcess.WorkingSet64; There’s a whole host of other process memory properties besides WorkingSet64 check out the “memory related” ones … Read more
See this response by Jack Klein (see original post): The original C standard (ANSI 1989/ISO 1990) required that a compiler successfully translate at least one program containing at least one example of a set of environmental limits. One of those limits was being able to create an object of at least 32,767 bytes. This minimum … Read more
The configuration for the memory_limit of PHP running as an Apache module to server webpages has to take into consideration how many Apache process you can have at the same time on the machine — see the MaxClients configuration option for Apache. If MaxClients is 100 and you have 2,000 MB of RAM, a very … Read more
From IEEE 1003.1: The mmap() function shall establish a mapping between a process’ address space and a file, shared memory object, or [TYM] typed memory object. It needs all the virtual address space because that’s exactly what mmap() does. The fact that it isn’t really running out of memory doesn’t matter – you can’t map … Read more
Like this: void * p = (void *)0x28ff44; Or if you want it as a char *: char * p = (char *)0x28ff44; …etc. If you’re pointing to something you really, really aren’t meant to change, add a const: const void * p = (const void *)0x28ff44; const char * p = (const char *)0x28ff44; … Read more
There are two places where variables can be put in memory. When you create a variable like this: int a; char c; char d[16]; The variables are created in the “stack“. Stack variables are automatically freed when they go out of scope (that is, when the code can’t reach them anymore). You might hear them … Read more