Heap fragmentation in 64 bit land
64-bit, c++, heap-fragmentation
Solution
Is this still an issue with a 64 bit address space?
No, it is not still an issue.
You are correct that it was an issue on 32-bit systems, but it no longer is an issue on 64-bit systems.
The virtual address space is so large on 64-bit systems (2^48 bytes at the moment on todays x86_64 processors, and set to increase gradually to 2^64 as new x86_64 processors come out), that running out of contiguous virtual address space due to fragmentation is practically impossible (for all but some highly contrived corner cases).
(It is a common error of intuition caused by the fact that 64 is "only" double 32, that causes people to think that a 64-bit address space is somehow roughly double a 32-bit one. In fact a full 64-bit address space is 4 billion times as big as a 32-bit address space.)
Put another way if it took your 32-bit daemon one week to fragment to a stage where it couldn't allocate an x byte block, than it would take at minimum one thousand years to fragment today's x86_64 processors 48-bit address spaces, and it would take 80 million years to fragment the future planned full 64-bit address space.
Problem
In the past, when I've worked on long-running C++ daemons I've had to deal with heap fragmentation issues. Tricks like keeping a pool of my large allocations were necessary to keep from running out of contiguous heap space. Is this still an issue with a 64 bit address space? Perf is not a concern for me, so I would prefer to simplify my code and not deal with things like buffer pools anymore. Does anyone have any experience or stories about this issue? I'm using Linux, but I imagine many of the same issues apply to Windows.