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 [off-list ref] wrote:

On Mon, 13 May 2013 14:11:22 -0500, Sergio Andr said:

quoted

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.