Re: mapping user space buffer to kernel address space

[Andrea Arcangeli]

On Tue, Oct 17, 2000 at 02:04:10PM -0700, Linus Torvalds wrote:
> It so happens that the vmscan stuff won't ever remove a physical page
> mapping, but that's simply because such a page CANNOT be swapped out. How

So if I write a mechanism that allows those driver-private-pages that are used
for DMA of a soundcard to be swapped out, then you would remove the
PG_referenced bitflag from them too?

What sense it has to start to writeout to disk a page that is under DMA when
you don't know if this page is getting changed under the swapout? Furthmore
despite of the swapout I/O those pages can't be freed until we run unmap_kiobuf.

> would you swap out the PCI space?

(minor note: that's not PCI space (the pci space case is handled by the
!VALID_PAGE(page) check). That's normal kernel memory exported to userspace
handled by the PageReserved(page) check.)

Andrea
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