[RFC] shrinking struct page (part of page pool)

[Byungchul Park <byungchul@sk.com>]

Hi guys,

I'm looking at network's page pool code to help 'shrinking struct page'
project by Matthew Wilcox.  See the following link:

   https://kernelnewbies.org/MatthewWilcox/Memdescs/Path

My first goal is to remove fields for page pool from struct page like:

   struct {	/* page_pool used by netstack */
	/**
	 * @pp_magic: magic value to avoid recycling non
	 * page_pool allocated pages.
	 */
	unsigned long pp_magic;
	struct page_pool *pp;
	unsigned long _pp_mapping_pad;
	unsigned long dma_addr;
	atomic_long_t pp_ref_count;
   };

Fortunately, many prerequisite works have been done by Mina but I guess
he or she has done it for other purpose than 'shrinking struct page'.

I'd like to just finalize the work so that the fields above can be
removed from struct page.  However, I need to resolve a curiousity
before starting.

   Network guys already introduced a sperate strcut, struct net_iov,
   to overlay the interesting fields.  However, another separate struct
   for system memory might be also needed e.g. struct bump so that
   struct net_iov and struct bump can be overlayed depending on the
   source:

   struct bump {
	unsigned long _page_flags;
	unsigned long bump_magic;
	struct page_pool *bump_pp;
	unsigned long _pp_mapping_pad;
	unsigned long dma_addr;
	atomic_long_t bump_ref_count;
	unsigned int _page_type;
	atomic_t _refcount;
   };

To netwrok guys, any thoughts on it?
To Willy, do I understand correctly your direction?

Plus, it's a quite another issue but I'm curious, that is, what do you
guys think about moving the bump allocator(= page pool) code from
network to mm?  I'd like to start on the work once gathering opinion
from both Willy and network guys.

	Byungchul