Linus Torvalds wrote:
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.
Oh that's true, I forgot. So the many small files case will often have
as much d_lock activity as tree_lock.
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.
Yes I see. Perhaps a seqlock could do the trick (hmm, there already is one),
however we still have to increment the refcount, so there'll always be a
shared cacheline.
--
SUSE Labs, Novell Inc.
Send instant messages to your online friends http://au.messenger.yahoo.com
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
