Re: Pagecache: find_or_create_page does not call a proper page allocator function

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 24 Apr 2007 13:30:33 -0700 (PDT) Christoph Lameter <clameter@sgi.com> wrote:

> > > If the system has both high memory and normal memory then only allocations 
> > > to highmemory are subject to memory policies etc etc. The block device 
> > > allocations would be in zone normal/dma and thus be exempt from NUMA 
> > > placement.
> > 
> > Please just point us to the line where sys_move_pages enforces this.
> 
> It does not. It will happily move the pages into highmem. The filesystem 
> cannot expect the page to remain in the same zone without holding a 
> reference count. Swap may also move pages between zones. There is nothing 
> special in what page migration does here.
> 
> I would say that the filesystem is broke if it has such expectations 
> regardless of page migration.

Others disagree ;)

The filesystem has *told* the core kernel what its allocation constraints
are by setting up mapping_gfp_mask().  If the core kernel stops honouring
that request then it is core kernel which is broken.