Willem de Bruijn <willemdebruijn.ker...@gmail.com> wrote: > > +#ifdef CONFIG_SKB_EXTENSIONS > > + __u8 active_extensions; > > +#endif > > This byte could be saved by moving the bits to the first byte of the > new extension.
I tried to do this, but could not resolve following problem: - extensions a and b are active - skb is cloned - extension a is to be disabled In this patch series, we can just clear the 'a' bit from from clone->active_extensions. But if its part of the extension itself, we must first need to be able to duplicate the extension blob before we can disable the extension, which means that attempt to disable an extension would now fail on -ENOMEM. I think disabling should always work. (its not a problem at the moment for either secpath or bridge as both use distinct pointers in sk_buff). > The likely cold cacheline now needs to be checked, but > only if the pointer is non-NULL. The upside of the 'active_extension' member is that we can keep the pointer in uninitialized state for the active_extensions == 0 case, i.e., when allocating a new skb skb->extensions is not initialized. > If exclusively using accessor > functions to access the struct, even this can be avoided if encoding > the first 3 or 7 active extensions in the pointer itself. Yes, that would work, but requires to init the pointer on skb allocation plus a few tricks to align the allocation so we have three bits to use on arches where kmalloc doesn't guarantee 8-byte-aligned pointers. Would also need a 'plan b' in place when extension number 4 arrives.
