On Fri, 12 Apr 2024 13:49:12 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote:
> On Fri, Apr 12, 2024 at 1:39 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
> >
> > On Fri, 12 Apr 2024 12:47:55 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote:
> > > 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.
> >
> >
> > The page pool needs to do the dma by the DMA APIs.
> > So we can not use the page pool directly.
>
> I found this:
>
> define PP_FLAG_DMA_MAP BIT(0) /* Should page_pool do the DMA
> * map/unmap
You are right. I missed this. I will try.
Thanks.
>
> It seems to work here?
>
> Thanks
>
> >
> > Thanks.
> >
> >
> > >
> > > Thanks
> > >
> >
>
