What is malloc doing, anyway?

Automated excerpt

When no free chunk fits, grow_heap moves the program break up in 64 KiB steps using sbrk and puts the new space on the free list as one chunk. Whether a free chunk still costs RAM depends on when the kernel puts physical memory behind an address. A live chunk holds the break above it, so every free chunk below it stays resident, as the 1 MiB block did here.

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