Re: [RFC PATCH net-next v1 4/4] net: page_pool: use netmem_t instead of struct page in API
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From: Mina Almasry <hidden>
Date: 2023-12-21 21:22:43
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On Thu, Dec 21, 2023 at 3:32 AM Yunsheng Lin [off-list ref] wrote:
On 2023/12/20 11:01, Mina Almasry wrote: ...quoted
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Perhaps we should aim to not export netmem_to_page(), prevent modules from accessing it directly.+1.I looked into this, but it turns out it's a slightly bigger change that needs some refactoring to make it work. There are few places where I believe I need to add netmem_to_page() that are exposed to the drivers via inline helpers, these are: - skb_frag_page(), which returns NULL if the netmem is not a page, but needs to do a netmem_to_page() to return the page otherwise.Is it possible to introduce something like skb_frag_netmem() for netmem? so that we can keep most existing users of skb_frag_page() unchanged and avoid adding additional checking overhead for existing users.
In my experience most current skb_frag_page() users need specifically the struct page*. Example is illegal_highdma() which PageHighMem(skb_frag_page()) But RFC v5 adds skb_frag_netmem() for callsites that want a netmem and don't care about specifically a page: https://patchwork.kernel.org/project/netdevbpf/patch/20231218024024.3516870-10-almasrymina@google.com/
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- The helpers inside skb_add_rx_frag(), which needs to do a netmem_to_page() to set skb->pfmemalloc.Similar as above, perhaps introduce something like skb_add_rx_netmem_frag()?
Yes, v3 of this series adds skb_add_rx_frag_netmem(): https://patchwork.kernel.org/project/netdevbpf/patch/20231220214505.2303297-4-almasrymina@google.com/
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- Some of the page_pool APIs are exposed to the drivers as static inline helpers, and if I want the page_pool to use netmem internally the page_pool needs to do a netmem_to_page() in these helpers. The refactor is not an issue, but I was wondering if not exporting netmem_to_page() was worth moving the code around. I was thinking in the interim until netmem is adopted and has actual driver users we may prefer to just add a comment on the netmem_to_page() helper that says 'try not to use this directly and use the netmem helpers instead'.
-- Thanks, Mina