Re: [PATCH net-next v12 05/13] page_pool: convert to use netmem

Paul Barker
2024-06-13T08:36:28Z

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On 13/06/2024 02:35, Mina Almasry wrote:
> Abstrace the memory type from the page_pool so we can later add support

s/Abstrace/Abstract/

> for new memory types. Convert the page_pool to use the new netmem type
> abstraction, rather than use struct page directly.
>
> As of this patch the netmem type is a no-op abstraction: it's always a
> struct page underneath. All the page pool internals are converted to
> use struct netmem instead of struct page, and the page pool now exports
> 2 APIs:
>
> 1. The existing struct page API.
> 2. The new struct netmem API.
>
> Keeping the existing API is transitional; we do not want to refactor all
> the current drivers using the page pool at once.
>
> The netmem abstraction is currently a no-op. The page_pool uses
> page_to_netmem() to convert allocated pages to netmem, and uses
> netmem_to_page() to convert the netmem back to pages to pass to mm APIs,
>
> Follow up patches to this series add non-paged netmem support to the
> page_pool. This change is factored out on its own to limit the code
> churn to this 1 patch, for ease of code review.
>
> Signed-off-by: Mina Almasry <almasrymina@google.com>
>
> ---
>
> v12:
> - Fix allmodconfig build error. Very recently renesas/ravb_main.c added
> a dependency on page_pool that I missed in my rebase. The dependency
> calls page_pool_alloc() directly as it wants to set a custom gfp_mask,
> which is unique as all other drivers call a wrapper to that function.
> Fix it by adding netmem_to_page() in the driver.> - Fix printing netmem trace printing (Pavel).
>
> v11:
> - Fix typing to remove sparse warning. (Paolo/Steven)
>
> v9:
> - Fix sparse error (Simon).
>
> v8:
> - Fix napi_pp_put_page() taking netmem instead of page to fix
> patch-by-patch build error.
> - Add net/netmem.h include in this patch to fix patch-by-patch build
> error.
>
> v6:
>
> - Rebased on top of the merged netmem_ref type.
>
> Cc: linux-mm@kvack.org
> Cc: Matthew Wilcox <willy@infradead.org>
>
> ---
> drivers/net/ethernet/renesas/ravb_main.c | 5 +-
> include/linux/skbuff_ref.h | 4 +-
> include/net/netmem.h | 15 ++
> include/net/page_pool/helpers.h | 120 ++++++---
> include/net/page_pool/types.h | 14 +-
> include/trace/events/page_pool.h | 30 +--
> net/bpf/test_run.c | 5 +-
> net/core/page_pool.c | 304 ++++++++++++-----------
> net/core/skbuff.c | 8 +-
> 9 files changed, 305 insertions(+), 200 deletions(-)
>
> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index c1546b916e4ef..093236ebfeecb 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> @@ -303,8 +303,9 @@ ravb_alloc_rx_buffer(struct net_device *ndev, int q, u32 entry, gfp_t gfp_mask,
>
> rx_buff = &priv->rx_buffers[q][entry];
> size = info->rx_buffer_size;
> - rx_buff->page = page_pool_alloc(priv->rx_pool[q], &rx_buff->offset,
> - &size, gfp_mask);
> + rx_buff->page = netmem_to_page(page_pool_alloc(priv->rx_pool[q],
> + &rx_buff->offset,
> + &size, gfp_mask));
> if (unlikely(!rx_buff->page)) {
> /* We just set the data size to 0 for a failed mapping which
> * should prevent DMA from happening...

[snip]

>
> -static inline struct page *page_pool_alloc(struct page_pool *pool,
> - unsigned int *offset,
> - unsigned int *size, gfp_t gfp)
> +static inline netmem_ref page_pool_alloc(struct page_pool *pool,
> + unsigned int *offset,
> + unsigned int *size, gfp_t gfp)
> {
> unsigned int max_size = PAGE_SIZE << pool->p.order;
> - struct page *page;
> + netmem_ref netmem;
>
> if ((*size << 1) > max_size) {
> *size = max_size;
> *offset = 0;
> - return page_pool_alloc_pages(pool, gfp);
> + return page_pool_alloc_netmem(pool, gfp);
> }
>
> - page = page_pool_alloc_frag(pool, offset, *size, gfp);
> - if (unlikely(!page))
> - return NULL;
> + netmem = page_pool_alloc_frag_netmem(pool, offset, *size, gfp);
> + if (unlikely(!netmem))
> + return 0;
>
> /* There is very likely not enough space for another fragment, so append
> * the remaining size to the current fragment to avoid truesize
> @@ -140,7 +142,7 @@ static inline struct page *page_pool_alloc(struct page_pool *pool,
> pool->frag_offset = max_size;
> }
>
> - return page;
> + return netmem;
> }
>
> /**
> @@ -154,7 +156,7 @@ static inline struct page *page_pool_alloc(struct page_pool *pool,
> * utilization and performance penalty.
> *
> * Return:
> - * Return allocated page or page fragment, otherwise return NULL.
> + * Return allocated page or page fragment, otherwise return 0.
> */
> static inline struct page *page_pool_dev_alloc(struct page_pool *pool,
> unsigned int *offset,
> @@ -162,7 +164,7 @@ static inline struct page *page_pool_dev_alloc(struct page_pool *pool,
> {
> gfp_t gfp = (GFP_ATOMIC | __GFP_NOWARN);
>
> - return page_pool_alloc(pool, offset, size, gfp);
> + return netmem_to_page(page_pool_alloc(pool, offset, size, gfp));
> }

I find this API change confusing - why should page_pool_alloc() return a
netmem_ref but page_pool_dev_alloc() return a struct page *?

Is there any reason to change page_pool_alloc() anyway? It calls
page_pool_alloc_pages() or page_pool_alloc_frag() as appropriate, both
of which your patch already converts to wrappers around the appropriate
_netmem() functions. In all instances where page_pool_alloc() is called
in this patch, you wrap it with netmem_to_page() anyway, there are no
calls to page_pool_alloc() added which actually want a netmem_ref.

Thanks,

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Paul Barker

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