memory leak problem concerning linux OS and htop command

Question

I am testing my C code and detecting memory leak. This piece of code has two functions:

• one of which is to initialize a struct context and allocate momory.
• the other is to finalize this struct context and release memory

I make a loop over these 2 functions like below:

struct context = NULL;
while (1) {

    initialize(&context);
    sleep(30);
    finalize(&context);
    sleep(30);

}

And then, I use the htop to monitor the memory leak and get the results below:

VIRT RES   -> VIRT RES
745M 78588 -> 126M 24752
672M 79112 -> 281M 51072
671M 81224 -> 281M 55300
671M 81224 -> 281M 55300
671M 81252 -> 281M 55332
671M 96488 -> 281M 70560
671M 102M  -> 281M 79368
671M 102M  -> 281M 79376
671M 109M  -> 281M 85724
671M 111M  -> 281M 88152

• The table consists of 10 lines. every line is the change of memory in one loop.
• The left part is the memory state when I initialized the context, and the right part is the memory state when I finalized and released the context.
• I recorded VIRT and RES column number in every state.
• As shown above, VIRT the program occupied is a fixed number: 671M(when initialized) and 281M(when released). But the RES is gradually increasing by every loop.

My question is: Is this called memory leak?