On Fri, May 14, 2021 at 04:31:50PM +0800, Yunsheng Lin wrote: > On 2021/5/14 15:36, Ilias Apalodimas wrote: > > [...] > >>> + return false; > >>> + > >>> + pp = (struct page_pool *)page->pp; > >>> + > >>> + /* Driver set this to memory recycling info. Reset it on recycle. > >>> + * This will *not* work for NIC using a split-page memory model. > >>> + * The page will be returned to the pool here regardless of the > >>> + * 'flipped' fragment being in use or not. > >>> + */ > >>> + page->pp = NULL; > >> > >> Why not only clear the page->pp when the page can not be recycled > >> by the page pool? so that we do not need to set and clear it every > >> time the page is recycled。 > >> > > > > If the page cannot be recycled, page->pp will not probably be set to begin > > with. Since we don't embed the feature in page_pool and we require the > > driver to explicitly enable it, as part of the 'skb flow', I'd rather keep > > it as is. When we set/clear the page->pp, the page is probably already in > > cache, so I doubt this will have any measurable impact. > > The point is that we already have the skb->pp_recycle to let driver to > explicitly enable recycling, as part of the 'skb flow, if the page pool keep > the page->pp while it owns the page, then the driver may only need to call > one skb_mark_for_recycle() for a skb, instead of call skb_mark_for_recycle() > for each page frag of a skb. > The driver is meant to call skb_mark_for_recycle for the skb and page_pool_store_mem_info() for the fragments (in order to store page->pp). Nothing bad will happen if you call skb_mark_for_recycle on a frag though, but in any case you need to store the page_pool pointer of each frag to struct page. > Maybe we can add a parameter in "struct page_pool_params" to let driver > to decide if the page pool ptr is stored in page->pp while the page pool > owns the page? Then you'd have to check the page pool config before saving the meta-data, and you would have to make the skb path aware of that as well (I assume you mean replace pp_recycle with this?). If not and you just want to add an extra flag on page_pool_params and be able to enable recycling depending on that flag, we just add a patch afterwards. I am not sure we need an extra if for each packet though. > > Another thing accured to me is that if the driver use page from the > page pool to form a skb, and it does not call skb_mark_for_recycle(), > then there will be resource leaking, right? if yes, it seems the > skb_mark_for_recycle() call does not seems to add any value? > Not really, the driver has 2 choices: - call page_pool_release_page() once it receives the payload. That will clean up dma mappings (if page pool is responsible for them) and free the buffer - call skb_mark_for_recycle(). Which will end up recycling the buffer. If you call none of those, you'd leak a page, but that's a driver bug. patches [4/5, 5/5] do that for two marvell drivers. I really want to make drivers opt-in in the feature instead of always enabling it. Thanks /Ilias > > > > >>> + page_pool_put_full_page(pp, virt_to_head_page(data), false); > >>> + > >>> C(end); > > > > [...] > >
