On Tue, 27 Jun 2023, Matthew Wilcox wrote:

On Mon, Jun 26, 2023 at 09:44:08PM -0700, Hugh Dickins wrote:

quoted

On Mon, 26 Jun 2023, Vishal Moola (Oracle) wrote:

quoted

The MM subsystem is trying to shrink struct page. This patchset
introduces a memory descriptor for page table tracking - struct ptdesc.

...

quoted

 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:

quoted

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.

Thank you, but I can adapt.  That was not my point:
I'm claiming this patchset is ~2-3 years ahead of its time.

I think you can see the advantage of the destination, so I don't think
you're against that.

Maybe - I have some scepticism, but I'll be happy for that to be dissolved.

Are you opposed to the sequencing of the work to
get us there?  I'd be happy to discuss another way to do it.

Yes, I'm opposed to churn for no benefit.

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.

That sounded much better, at first: churn serving good purpose.  But now
I suspect you're offering to dynamically allocate a ptdesc, in addition
to the struct page of the page table(s) itself, which will be wasted:
more memory consumption to no advantage.  If that's so, no thanks.

Hugh

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