Re: [patch 2] Xen core patch : arch_free_page return value

[Dave Hansen]

On Wed, 2004-11-17 at 17:19, Ian Pratt wrote:
> > On Wed, 2004-11-17 at 15:48, Ian Pratt wrote:
> > > This patch adds a return value to the existing arch_free_page function
> > > that indicates whether the normal free routine still has work to
> > > do. The only architecture that currently uses arch_free_page is arch
> > > 'um'. arch-xen needs this for 'foreign pages' - pages that don't
> > > belong to the page allocator but are instead managed by custom
> > > allocators.
> > 
> > But, you're modifying page allocator functions to do this.  Why would
> > you call __free_pages_ok() on a page that didn't belong to the page
> > allocator?
> 
> Pages that have been allocated by our custom allocators get passed
> into standard linux subsystems where we get no control over how
> they're freed.

OK, then how are they allocated?  Are they only allocated by your
special drivers or in your architecture?

I think allowing this is weird:

        foo = special_zen_malloc();
        bar = kmalloc();
        kfree(foo);
        kfree(bar);
        
Shoudn't it be

	special_zen_free(free);?
        
BTW, your arch-specific definition of PG_foreign is a little goofy.  If
you need the bit, then put it in page-flags.h now.  The memory hotplug
people have an evil plan to consume all unused bits in page->flags
(determined at compile-time) and that little gem will certainly break
it.  

It's great that you contained stuff to your architecture, but little
bits like the page-flags thing don't make me think you've done it for
real, only hacked around it :)

-- Dave

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