Re: [PATCH 0/17] Sliding window mmap for packfiles.

From: Linus Torvalds <torvalds@osdl.org>
Date: Dec 24, 2006, 09:29 UTC
Message-ID: <Pine.LNX.4.64.0612240126380.3671@woody.osdl.org>
In-Reply-To: <38b2ab8a0612240056k152344ael891e9b0b9f8cbc47@mail.gmail.com>

On Sun, 24 Dec 2006, Francis Moreau wrote:

> 
> Just out of curiosity, do you mean that there are some OS running on
> 32 bits machines which allow 4GiB size of virtual memory within a
> single process ? If so, could you give an example of such OS ?

Actually, Linux will do it on certain architectures (some architectures have separate "address spaces" for kernel and user). And even on x86, if you apply the (insane) 4GB patches, user space will actually have almost all of the 4GB, because there's only a _tiny_ trampoline thing that switches the whole page table around that is kernel-mapped and takes away from the 4GB thing.

In practice, though, most 32-bit architectures will have between 1-3GB of user virtual memory. And obviously stack space, binaries, heap etc take up space, so you often end up with with just ~0.5 GB of actual dependable contiguous virtual memory.

			Linus