Re: [PATCH linux-next v3] mm, page_pool: introduce a new page type for page pool in page type

On Fri, Aug 01, 2025 at 04:08:05PM -0700, Jakub Kicinski wrote:

On Tue, 29 Jul 2025 20:02:10 +0900 Byungchul Park wrote:

quoted

[PATCH linux-next v3] mm, page_pool: introduce a new page type for page pool in page type

linux-next does not accept patches. This has to go either via networking or MM.

Yeah.  That's what I found.  Thanks for the confirmation.

quoted

-     if (unlikely(page_has_type(page)))
+     if (unlikely(page_has_type(page))) {

Maybe add :

                /* networking expects to clear its page type before releasing */

I will.

quoted

+             WARN_ON_ONCE(PageNetpp(page));
              /* Reset the page_type (which overlays _mapcount) */
              page->page_type = UINT_MAX;
+     }

quoted

 static inline bool netmem_is_pp(netmem_ref netmem)
 {
-     return (netmem_get_pp_magic(netmem) & PP_MAGIC_MASK) == PP_SIGNATURE;
+     /* Use ->pp for net_iov to identify if it's pp,

Please try to use precise language, this code is confusing as is.
net_iov may _belong_ to a page pool.

        * which requires that non-pp net_iov should have ->pp NULL'd.

Thank you.  I will.

I don't think this adds any information.

quoted

+      */
+     if (netmem_is_net_iov(netmem))
+             return !!__netmem_clear_lsb(netmem)->pp;
+
+     /* For system memory, page type bit in struct page can be used

"page type bit" -> "page type", it's not a bit.

quoted

+      * to identify if it's pp.

... to identify pages which belong to a page pool.

I will.

quoted

+      */
+     return PageNetpp(__netmem_to_page(netmem));
 }

 static inline void netmem_set_pp(netmem_ref netmem, struct page_pool *pool)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 05e2e22a8f7c..37eeab76c41c 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c

@@ -654,7 +654,6 @@ s32 page_pool_inflight(const struct page_pool *pool, bool strict)
 void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem)
 {
      netmem_set_pp(netmem, pool);
-     netmem_or_pp_magic(netmem, PP_SIGNATURE);

      /* Ensuring all pages have been split into one fragment initially:
       * page_pool_set_pp_info() is only called once for every page when it

@@ -665,12 +664,19 @@ void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem)
      page_pool_fragment_netmem(netmem, 1);
      if (pool->has_init_callback)
              pool->slow.init_callback(netmem, pool->slow.init_arg);
+
+     /* If it's page-backed */

Please don't add obvious comments.

I added the comment since it's _not_ obvious.  !net_iov means it's not
net_iov, not it's page-backed.  However, since you, as the maintainer,
are okay, I will remove it.  Thanks.

	Byungchul

quoted

+     if (!netmem_is_net_iov(netmem))
+             __SetPageNetpp(__netmem_to_page(netmem));