[announce] vfs-scale git tree update

From: Nick Piggin
Date: Wed Jan 05 2011 - 05:25:49 EST

Git tree is here:


Branch is:


Changes since last posting:
* Updated to 2.6.37 (Documentation/filesystems/Locking clash)
* Switch names of vfsmount scalable counter helpers suggested by Andreas
* Most significant are changes in Documentation/filesystems/path-lookup.txt
attempt to make it more readable, consistent and informative. Add some
interesting rcu-walk path lookup success and behaviour statistics.

* Linus is planning to merge. It's never too late for review, though.
* linux-next has been uneventful, but I don't think it nearly covers all
interesting and fiddly use cases.
* Still has the barrier-less __seqcount optimisation that Linus didn't
like; I like the idea of a seqcount-switch API, but it just didn't
seem to fit well here. Let's leave that on the todo list?

Future dcache / name lookup work:
* Per-zone LRUs. Patch is simple and ready, but performance bisecting
might be a bit easier if we hold off. Also inode LRUs should be done at
the same time.
* Filesystems will need to start implementing rcu-walk aware dentry
and permission ops. They've got simple examples to follow.
* Rename scaling. The rename seqlock can explode on large systems,
getting into strange conditions where lookup performance crashes.
It is also a global lock for renames. Quite simple to break it up and
fix lookup performance and provide linear vfs scalability for parallel
same-directory renames (if they are in different directories). Doesn't
need to be merged yet, though.
* Further optimise name string copying and comparison (may be as much as
10-20% in that).
* rcu-walk for symlinks. A bit tricky, not impossible.

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