Is there a way to make sure an array variable (unsigned int*) will be in memory?

I need to set some default value for all entires in a very large array. It takes me quite long time (110-120 ms) and i suspect it happens beca开发者_高级运维use of misses in memory.

I use memset/std:fill to set the default value. Is there a way to make sure that the array will reside in memory before the memset/fill?

Assuming this is a large memory-mapped file, you can use the madvise() libc call with the MADV_WILLNEED argument to hint to the OS that you'll be wanting to access the region mentioned soon.

However YMMV, as the array needs to be large enough that the benefit of the resulting syscall isn't outweighed by the cost of making the call.

You can lock memory at per-page granuality using mlock, though only up to a fixed amount (I'm not sure what the limit is on OS X, but you can check it using getrlimit with RLIMIT_MEMLOCK).

Most likely you have a multiple core processor and functions like memset actually degrade in performance when not used on single core CPUs. It's possible that mutex locking are causing the slowdown. Try allocating memory on the stack instead of dynamic memory. Since it's a very large array then I would experiment making my own memory manager and store segments of it in multiple threads (but that's just an idea I had after reading an article fast). A standard way of doing it would be to use one memory allocator per thread. In any case I would look into something else than memset.

Maybe the following aticle would help