Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > David, Linus, do you see any problems with that? To me it looks saner > that way and as cheap as the current code, but I might be missing something > here... You're effectively converting to this: read d_seq.sequence smp_rmb() read d_inode, d_flags smp_rmb() check d_seq.sequence in the read path and this: write d_seq.sequence smp_wmb() write d_inode, d_flags smp_wmb() write d_seq.sequence This should work - especially if we're wangling these sequence points anyway, and so have to pay the barrier penalties whatever. In fact, you actually take a barrier out, I think. I have had a problem with getting the ordering of d_inode and d_flags right because of __d_clear_type_and_inode() where we're required to unset a dentry so that it can be repurposed[*] as a negative dentry rather than replacing it. This is something we for performance sake - and it's something we can only do if the dentry isn't referenced, whereas if we properly followed the RCU model, we would have to wait a grace period after delisting an unlinked dentry before we could repurpose it - but that significantly slows down rename, unlink and rmdir. [*] Al and I disagree on whether this is a reuse or merely a change of state. David -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
