Re: [PATCH v6 00/33] Split ptdesc from struct page

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Mon, Jun 26, 2023 at 09:44:08PM -0700, Hugh Dickins wrote:
> On Mon, 26 Jun 2023, Vishal Moola (Oracle) wrote:
> 
> > The MM subsystem is trying to shrink struct page. This patchset
> > introduces a memory descriptor for page table tracking - struct ptdesc.
> ...
> >  39 files changed, 686 insertions(+), 455 deletions(-)
> 
> I don't see the point of this patchset: to me it is just obfuscation of
> the present-day tight relationship between page table and struct page.
> 
> Matthew already explained:
> 
> > The intent is to get ptdescs to be dynamically allocated at some point
> > in the ~2-3 years out future when we have finished the folio project ...
> 
> So in a kindly mood, I'd say that this patchset is ahead of its time.
> But I can certainly adapt to it, if everyone else sees some point to it.

If you think this patchset is ahead of its time, we can certainly put
it on hold.  We're certainly prepared to redo it to be merged after your
current patch series.

I think you can see the advantage of the destination, so I don't think
you're against that.  Are you opposed to the sequencing of the work to
get us there?  I'd be happy to discuss another way to do it.

For example, we could dynamically allocate ptdescs right now.  We'd get
the benefit of having an arbitrary amount of space in the ptdesc,
although not the benefit of a smaller memmap until everything else is
also dynamically allocated.