Re: Folios for 5.15 request - Was: re: Folio discussion recap -

[Christoph Hellwig]

On Sat, Oct 23, 2021 at 03:22:35AM +0100, Matthew Wilcox wrote:
> You can see folios as a first step to disentangling some of the users
> of struct page.  It certainly won't be the last step.  But I'd really
> like to stop having theoretical discussions of memory types and get on
> with writing code.

Agreed.  I think folios are really important to sort out the mess
around compound pages ASAP.

I'm a lot more lukewarm on the other splits.  Yes, struct page is a
mess, but I'm not sure creating gazillions of new types solve that
mess.  Getting rid of a bunch of the crazy optimizations that abuse
struct page fields might a better first step - or rather after the
first step of folios which fix real bugs in compount handling and do
enable sane handling of compound pages in the page cache.

> If that means we modify the fs APIs again in twelve
> months to replace folios with file_mem, well, I'm OK with that.

I suspect we won't even need that so quickly if at all, but I'd rather
have a little more churn rather than blocking this important work
forever.