On Fri, 12 Apr 2024 12:47:55 +0800, Jason Wang <jasow...@redhat.com> wrote:
> On Thu, Apr 11, 2024 at 10:51 AM Xuan Zhuo <xuanz...@linux.alibaba.com> 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 <xuanz...@linux.alibaba.com>
> > ---
>
> 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.
The page pool needs to do the dma by the DMA APIs.
So we can not use the page pool directly.
Thanks.
>
> Thanks
>
