On Thu, Apr 11, 2024 at 10:51 AM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
>
> Now, we chain the pages of big mode by the page's private variable.
> But a subsequent patch aims to make the big mode to support
> premapped mode. This requires additional space to store the dma addr.
>
> Within the sub-struct that contains the 'private', there is no suitable
> variable for storing the DMA addr.
>
> struct { /* Page cache and anonymous pages */
> /**
> * @lru: Pageout list, eg. active_list protected by
> * lruvec->lru_lock. Sometimes used as a generic list
> * by the page owner.
> */
> union {
> struct list_head lru;
>
> /* Or, for the Unevictable "LRU list" slot */
> struct {
> /* Always even, to negate PageTail */
> void *__filler;
> /* Count page's or folio's mlocks */
> unsigned int mlock_count;
> };
>
> /* Or, free page */
> struct list_head buddy_list;
> struct list_head pcp_list;
> };
> /* See page-flags.h for PAGE_MAPPING_FLAGS */
> struct address_space *mapping;
> union {
> pgoff_t index; /* Our offset within mapping. */
> unsigned long share; /* share count for fsdax */
> };
> /**
> * @private: Mapping-private opaque data.
> * Usually used for buffer_heads if PagePrivate.
> * Used for swp_entry_t if PageSwapCache.
> * Indicates order in the buddy system if PageBuddy.
> */
> unsigned long private;
> };
>
> But within the page pool struct, we have a variable called
> dma_addr that is appropriate for storing dma addr.
> And that struct is used by netstack. That works to our advantage.
>
> 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;
> };
>
> On the other side, we should use variables from the same sub-struct.
> So this patch replaces the "private" with "pp".
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> ---
> drivers/net/virtio_net.c | 27 +++++++++++++++------------
> 1 file changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c22d1118a133..4446fb54de6d 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -48,6 +48,9 @@ module_param(napi_tx, bool, 0644);
>
> #define VIRTIO_XDP_FLAG BIT(0)
>
> +#define page_chain_next(p) ((struct page *)((p)->pp))
> +#define page_chain_add(p, n) ((p)->pp = (void *)n)
> +
> /* RX packet size EWMA. The average packet size is used to determine the packet
> * buffer size when refilling RX rings. As the entire RX ring may be refilled
> * at once, the weight is chosen so that the EWMA will be insensitive to short-
> @@ -191,7 +194,7 @@ struct receive_queue {
>
> struct virtnet_interrupt_coalesce intr_coal;
>
> - /* Chain pages by the private ptr. */
> + /* Chain pages by the page's pp struct. */
> struct page *pages;
>
> /* Average packet length for mergeable receive buffers. */
> @@ -432,16 +435,16 @@ skb_vnet_common_hdr(struct sk_buff *skb)
> }
>
> /*
> - * private is used to chain pages for big packets, put the whole
> - * most recent used list in the beginning for reuse
> + * put the whole most recent used list in the beginning for reuse
> */
While at this, let's explain the pp is used to chain pages or we can
do it on the definition of page_chain_add().
Others look good.
Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
Thanks
