c - Minimizing the amount of malloc() calls improves performance?

Question

Consider two applications: one (num. 1) that invokes malloc() many times, and the other (num. 2) that invokes malloc() few times. Both applications allocate the same amount of memory (assume 100MB).
For which application the next malloc() call will be faster, #1 or #2?
In other words: Does malloc() have an index of allocated locations in memory?

Answer 1

You asked 2 questions:

• for which application the next malloc() call will be faster, #1 or #2?
• In other words: Does malloc() have an index of allocated locations in memory?

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You've implied that they are the same question, but they are not. The answer to the latter question is YES.

As for which will be faster, it is impossible to say. It depends on the allocator algorithm, the machine state, the fragmentation in the current process, and so on.

Your idea is sound, though: you should think about how malloc usage will affect performance. There was once an app I wrote that used lots of little blobs of memory, each allocated with malloc(). It worked correctly but was slow. I replaced the many calls to malloc with just one, and then sliced up that large block within my app. It was much much faster.

I don't recommend this approach; it's just an illustration of the point that malloc usage can materially affect performance.

My advice is to measure it.