C malloc, memory usage only when populating
c, malloc, memory-management
Solution
Short answer, no. On many OSs, when you call malloc, it doesn't directly allocate you the memory, but only when you access it.
From `malloc` man page:
By default, Linux follows an optimistic memory allocation strategy. This means that when malloc() returns non-NULL there is no guarantee that the memory really is available.
Problem
I'm allocating some space with malloc when my app starts. If I don't populate this variable top shows 0% of my memory used by this app, but if I start to populate this variable top begins to show increase usage of ram by the way I'm populating this array. So my question is: shouldn't top show this space allocated by malloc as an used space of my app? Why it only show increase of RAM usage from my app when I populate this variable? I'm at Ubuntu 10.10 64bits. Here is the code that populates it: ``` char pack(uint64_t list, char bits, uint64_t *list_compressed, char control, uint64_t *index){ uint64_t a, rest; if(control == 0){ a = list; } else{ rest = list >> (64 - control); a = (control == 64 ? list_compressed[*index] : list_compressed[*index] + (list << control)); if(control + bits >= 64){ control = control - 64; //list_compressed[*index] = a; (*index)++; a = rest; } } //list_compressed[*index] = a; control = control + bits; return control; } ``` The "malloqued" variable is list_compressed. If I uncomment the list_compressed population the ram usage is increased, if I keep it commented the usage is 0%.