Re: [RFC PATCH net-next] page_pool: Track DMA-mapped pages and unmap them when destroying the pool

[Matthew Wilcox <willy@infradead.org>]

On Tue, Mar 11, 2025 at 08:25:25PM +0800, Yunsheng Lin wrote:
> > struct page {
> > 	unsigned long flags;
> > 	unsigned long memdesc;
> 
> It seems there may be memory behind the above 'memdesc' with different size
> and layout for different subsystem?

Yes.

> I am not sure if I understand the case of the same page might be handle in
> two subsystems concurrently or a page is allocated in one subsystem and
> then passed to be handled in other subsystem, for examlpe:
> page_pool owned page is mmap'ed into user space through tcp zero copy,
> see tcp_zerocopy_vm_insert_batch(), it seems the same page is handled in
> both networking/page_pool and vm subsystem?

It's not that arbitrary.  I mean, you could read all the documentation
I've written about this concept, listen to the talks I've given.  But
sure, you're a special fucking snowflake and deserve your own unique
explanation.