Re: Folio mapcount

[Mike Kravetz <mike.kravetz@oracle.com>]

On 01/24/23 18:13, Matthew Wilcox wrote:
> Once we get to the part of the folio journey where we have 
> one-pointer-per-page, we can't afford to maintain per-page state.
> Currently we maintain a per-page mapcount, and that will have to go. 
> We can maintain extra state for a multi-page folio, but it has to be a
> constant amount of extra state no matter how many pages are in the folio.
> 
> My proposal is that we maintain a single mapcount per folio, and its
> definition is the number of (vma, page table) tuples which have a
> reference to any pages in this folio.

Hi Matthew, finally took a look at this.  Can you clarify your definition of
'page table' here?  I think you are talking about all the entries within
one page table page?  Is that correct?  It certainly makes sense in this
context.

I have always thought of page table as the entire tree structure starting at
*pgd in the mm_struct.  So, I was a bit confused.  But, I now see elsewhere
that 'page table' may refer to either.
-- 
Mike Kravetz