Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online_page()

[Aneesh Kumar K.V]

On 6/14/19 10:38 PM, Jeff Moyer wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx> writes:
>
> > On 6/14/19 10:06 PM, Dan Williams wrote:
> > > On Fri, Jun 14, 2019 at 9:26 AM Aneesh Kumar K.V
> > > <aneesh.kumar@xxxxxxxxxxxxx> wrote:
> >
> > > > Why not let the arch
> > > > arch decide the SUBSECTION_SHIFT and default to one subsection per
> > > > section if arch is not enabled to work with subsection.
> > >
> > > Because that keeps the implementation from ever reaching a point where
> > > a namespace might be able to be moved from one arch to another. If we
> > > can squash these arch differences then we can have a common tool to
> > > initialize namespaces outside of the kernel. The one wrinkle is
> > > device-dax that wants to enforce the mapping size,
> >
> > The fsdax have a much bigger issue right? The file system block size
> > is the same as PAGE_SIZE and we can't make it portable across archs
> > that support different PAGE_SIZE?
>
> File system blocks are not tied to page size.  They can't be *bigger*
> than the page size currently, but they can be smaller.


ppc64 page size is 64K.

> Still, I don't see that as an arugment against trying to make the
> namespaces work across architectures.  Consider a user who only has
> sector mode namespaces.  We'd like that to work if at all possible.

agreed. I was trying to list out the challenges here.

-aneesh