карта страниц памяти (map pages of memory)
Возвращаемое значение (Return value)
Upon successful completion, the mmap() function shall return the
address at which the mapping was placed (pa); otherwise, it shall
return a value of MAP_FAILED and set errno to indicate the error.
The symbol MAP_FAILED is defined in the <sys/mman.h> header. No
successful return from mmap() shall return the value MAP_FAILED.
