Re: [PATCH 1/3] memory: extern memory_block_size_bytes and set_memory_block_size_order

[David Hildenbrand]

On 08.10.24 16:51, Gregory Price wrote:
> On Tue, Oct 08, 2024 at 04:03:37PM +0200, David Hildenbrand wrote:
> > On 08.10.24 06:43, Gregory Price wrote:
> > > On CXL systems, block alignment may be as small as 256MB, which may
> > > require a resize of the block size during initialization.  This is done
> > > in the ACPI driver, so the resize function need to be made available.
> > >
> > > Presently, only x86 provides the functionality to resize memory
> > > block sizes.  Wire up a weak stub for set_memory_block_size_order,
> > > similar to memory_block_size_bytes, that simply returns -ENODEV.
> > >
> > > Since set_memory_block_size_order is now extern, we also need to
> > > drop the __init macro.
> > >
> > > Signed-off-by: Gregory Price <gourry@xxxxxxxxxx>
> > > ---
> > >    arch/x86/mm/init_64.c  | 2 +-
> > >    drivers/base/memory.c  | 6 ++++++
> > >    include/linux/memory.h | 4 ++--
> > >    3 files changed, 9 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> > > index ff253648706f..6086f99449fa 100644
> > > --- a/arch/x86/mm/init_64.c
> > > +++ b/arch/x86/mm/init_64.c
> > > @@ -1424,7 +1424,7 @@ void mark_rodata_ro(void)
> > >    /* Adjustable memory block size */
> > >    static unsigned long set_memory_block_size;
> > > -int __init set_memory_block_size_order(unsigned int order)
> > > +int set_memory_block_size_order(unsigned int order)
> > >    {
> > >    	unsigned long size = 1UL << order;
> > > diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> > > index 67858eeb92ed..f9045642f69e 100644
> > > --- a/drivers/base/memory.c
> > > +++ b/drivers/base/memory.c
> > > @@ -110,6 +110,12 @@ static void memory_block_release(struct device *dev)
> > >    	kfree(mem);
> > >    }
> > > +int __weak set_memory_block_size_order(unsigned int order)
> > > +{
> > > +	return -ENODEV;
> > > +}
> > > +EXPORT_SYMBOL_GPL(set_memory_block_size_order);
> >
> > I can understand what you are trying to achieve, but letting arbitrary
> > modules mess with this sounds like a bad idea.
>
> I suppose the alternative is trying to scan the CEDT from inside each
> machine, rather than the ACPI driver?  Seems less maintainable.
>
> I don't entirely disagree with your comment.  I hummed and hawwed over
> externing this - hence the warning in the x86 machine.
>
> Open to better answers.

Maybe an interface to add more restrictions on the maximum size might be 
better (instead of setting the size/order, you would impose another 
upper limit). Just imagine having various users of such an interface ..

--
Cheers,

David / dhildenb