Messages in this thread | | | Date | Thu, 27 Apr 2006 08:12:28 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: Lockless page cache test results |
| |
On Thu, 27 Apr 2006, Nick Piggin wrote: > > > > Of course, with small files, the actual filename lookup is likely to be the > > real limiter. > > Although that's lockless so it scales. find_get_page will overtake it > at some point.
filename lookup is only lockless for independent files. You end up getting the "dentry->d_lock" for a successful lookup in the lookup path, so if you have multiple threads looking up the same files (or - MUCH more commonly - directories), you're not going to be lockless.
I don't know how we could improve it. I've several times thought that we _should_ be able to do the directory lookups under the rcu read lock and never touch their d_count or d_lock at all, but the locking against directory renaming depends very intimately on d_lock.
It is _possible_ that we should be able to handle it purely with just memory ordering rather than depending on d_lock. That would be wonderful.
Of course, we do actually scale pretty damn well already. I'm just saying that it's not perfect.
See __d_lookup() for details.
Linus - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |