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>
> ---
Instead of doing a customized version of page pool, can we simply
switch to use page pool for big mode instead? Then we don't need to
bother the dma stuffs.
Thanks
