Any way to reserve but not commit memory in linux?

linux memory-management virtualalloc
Eloff picture Eloff · May 6, 2010 · Viewed 15.8k times · Source

Windows has VirtualAlloc, which allows you to reserve a contiguous region of address space, but not actually use any physical memory. Later when you want to use it (or part of it) you call VirtualAlloc again to commit the region of previously reserved pages.

This is actually really useful, but I want to eventually port my application to linux - so I don't want to use it if I can't port it later. Does linux have a way to do this?

EDIT - Use Case

I'm thinking of allocating 4 GB or some such of virtual address space, but only committing it 64K at a time. This would give me a zero-copy way to grow an array up to 4 GB. Which is important, because the typical double the array size and copy introduces seemingly random unacceptable latency for very large arrays.

Answer

Ben Voigt picture Ben Voigt · May 6, 2010

mmap a special file, like /dev/zero (or use MAP_ANONYMOUS) as PROT_NONE, later use mprotect to commit.

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