Re: [PATCH v2 17/24] page_pool: Convert page_pool_return_skb_page() to use netmem

On Fri, Jan 06, 2023 at 09:16:25PM +0100, Jesper Dangaard Brouer wrote:

On 06/01/2023 17.53, Matthew Wilcox wrote:

quoted

On Fri, Jan 06, 2023 at 04:49:12PM +0100, Jesper Dangaard Brouer wrote:

quoted

On 05/01/2023 22.46, Matthew Wilcox (Oracle) wrote:

quoted

This function accesses the pagepool members of struct page directly,
so it needs to become netmem.  Add page_pool_put_full_netmem() and
page_pool_recycle_netmem().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
   include/net/page_pool.h | 14 +++++++++++++-
   net/core/page_pool.c    | 13 ++++++-------
   2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index fbb653c9f1da..126c04315929 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h

@@ -464,10 +464,16 @@ static inline void page_pool_put_page(struct page_pool *pool,
   }
   /* Same as above but will try to sync the entire area pool->max_len */
+static inline void page_pool_put_full_netmem(struct page_pool *pool,
+		struct netmem *nmem, bool allow_direct)
+{
+	page_pool_put_netmem(pool, nmem, -1, allow_direct);
+}
+
   static inline void page_pool_put_full_page(struct page_pool *pool,
   					   struct page *page, bool allow_direct)
   {
-	page_pool_put_page(pool, page, -1, allow_direct);
+	page_pool_put_full_netmem(pool, page_netmem(page), allow_direct);
   }
   /* Same as above but the caller must guarantee safe context. e.g NAPI */

@@ -477,6 +483,12 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
   	page_pool_put_full_page(pool, page, true);
   }
+static inline void page_pool_recycle_netmem(struct page_pool *pool,
+					    struct netmem *nmem)
+{
+	page_pool_put_full_netmem(pool, nmem, true);

                                               ^^^^

It is not clear in what context page_pool_recycle_netmem() will be used,
but I think the 'true' (allow_direct=true) might be wrong here.

It is only in limited special cases (RX-NAPI context) we can allow
direct return to the RX-alloc-cache.

Mmm.  It's a c'n'p of the previous function:

static inline void page_pool_recycle_direct(struct page_pool *pool,
                                             struct page *page)
{
         page_pool_put_full_page(pool, page, true);
}

so perhaps it's just badly named?

Yes, I think so.

Can we name it:
 page_pool_recycle_netmem_direct

And perhaps add a comment with a warning like:
 /* Caller must guarantee safe context. e.g NAPI */

Like the page_pool_recycle_direct() function has a comment.

I don't really like the new name you're proposing here.  Really,
page_pool_recycle_direct() is the perfect name, it just has the wrong
type.

I considered the attached megapatch, but I don't think that's a great
idea.

So here's what I'm planning instead:

    page_pool: Allow page_pool_recycle_direct() to take a netmem or a page

    With no better name for a variant of page_pool_recycle_direct() which
    takes a netmem instead of a page, use _Generic() to allow it to take
    either a page or a netmem argument.  It's a bit ugly, but maybe not
    the worst alternative?

    Signed-off-by: Matthew Wilcox (Oracle) [off-list ref]

diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index abe3822a1125..1eed8ed2dcc1 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h

@@ -477,12 +477,22 @@ static inline void page_pool_put_full_page(struct page_pool *pool,
 }

 /* Same as above but the caller must guarantee safe context. e.g NAPI */
-static inline void page_pool_recycle_direct(struct page_pool *pool,
+static inline void __page_pool_recycle_direct(struct page_pool *pool,
+                                           struct netmem *nmem)
+{
+       page_pool_put_full_netmem(pool, nmem, true);
+}
+
+static inline void __page_pool_recycle_page_direct(struct page_pool *pool,
                                            struct page *page)
 {
-       page_pool_put_full_page(pool, page, true);
+       page_pool_put_full_netmem(pool, page_netmem(page), true);
 }

+#define page_pool_recycle_direct(pool, mem)    _Generic((mem),         \
+       struct netmem *: __page_pool_recycle_direct(pool, (struct netmem *)mem),                \
+       struct page *:   __page_pool_recycle_page_direct(pool, (struct page *)mem))
+
 #define PAGE_POOL_DMA_USE_PP_FRAG_COUNT        \
                (sizeof(dma_addr_t) > sizeof(unsigned long))