On Mon, Aug 21, 2023 at 5:31 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > > On Sat, 19 Aug 2023 12:12:16 -0400 Willem de Bruijn wrote: > > :-) For the record, there is a prior version that added a separate type. > > > > I did not like the churn it brought and asked for this. > > It does end up looking cleaner that I personally expected, FWIW. > > > > Use of the LSB (or bits depending on alignment expectations) is a common > > > trick and already done in quite a few places in the networking stack. > > > This trick is essential to any realistic change here to incorporate gpu > > > memory; way too much code will have unnecessary churn without it. > > We'll end up needing the LSB trick either way, right? The only question > is whether the "if" is part of page pool or the caller of page pool. Indeed. Adding layering does not remove this. > Having seen zctap I'm afraid if we push this out of pp every provider > will end up re-implementing page pool's recycling/caching functionality > :( > > Maybe we need to "fork" the API? The device memory "ifs" are only needed > for data pages. Which means that we can retain a faster, "if-less" API > for headers and XDP. Or is that too much duplication? I don't think that would be faster. Just a different structuring of the code. We still need to take one of multiple paths for, say, page allocation (page_pool_alloc_pages). If having a struct page_pool and struct mem_pool, there would still be a type-based branch. But now either in every caller (yech), or in some thin shim layer. Why not just have it behind the existing API? That is what your memory provider does. The only difference now is that one of the providers really does not deal with pages. I think this multiplexing does not have to introduce performance regressions with well placed static_branch. Benchmarks and side-by-side comparison of assembly will have to verify that. Indirect function calls need to be avoided, of course, in favor of a type based switch. And unless the non_default_providers static branch is enabled, the default path is taken unconditionally. If it no longer is a pure page pool, maybe it can be renamed. I personally don't care.
