Mapping of ZONE_HIGHMEM in kernel address space in 32bit x86

[Sergio Andrés Gómez del Real]

Sure, I forgot what you said; precisely the mechanism allows to use
lots of linear space without necessarily allocating physical memory
(demand paging and the like).
What about the rest of what I said? Is it correct or is there
something wrong about it?
Thanks.

On 5/13/13, Valdis.Kletnieks at vt.edu <Valdis.Kletnieks at vt.edu> wrote:
> On Mon, 13 May 2013 14:11:22 -0500, Sergio Andr said:
>
>> 2. When user applications allocates memory, the kernel must allocate
>> virtual memory and physical memory, right?
>
> Wrong. If userspace allocates (say) 15M of memory, the kernel has every
> right
> to overcommit and not actually allocate either physical memory or backing
> page
> space for all 15M.  It instead maps it as a non-existent virtual address,
> and
> if/when the application actually touches the page, it generates a page
> fault,
> and *then* the kernel does the allocating of physical memory and maybe swap
> space.
>
>