linux-kernel - Re: [PATCH 0/9 v3] locks: avoid thundering-herd wake-ups

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Date:   Thu, 25 Oct 2018 12:04:01 -0400
From:   "J. Bruce Fields" <bfields@...ldses.org>
To:     NeilBrown <neilb@...e.com>
Cc:     Jeff Layton <jlayton@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Martin Wilck <mwilck@...e.de>, linux-fsdevel@...r.kernel.org,
        Frank Filz <ffilzlnx@...dspring.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/9 v3] locks: avoid thundering-herd wake-ups

On Wed, Oct 24, 2018 at 09:43:54AM +1100, NeilBrown wrote:
> This took longer that I had wanted, due to various reasons - sorry.
> And I'm now posting it in a merge window, which is not ideal.  I don't
> expect it to be included in this merge window and I won't be at all
> impatient for review, but I didn't want to delay it further.

Yes, apologies, I've been looking forward to finding out how this turned
out, but I'd like to track down a bug or two and also review Olga's copy
patches....  Bug me if I haven't gotten to this in a week or two.

I'd also be really interested in any details of the performance
experiments that you could share.

--b.

> 
> Testing found some problems, particularly the need to use
> locks_copy_lock in NFS.  And there was a small thinko in there that
> effectively removed all the speed gains :-(
> 
> But this version:
>  - shows excellent scalability with lots of threads on lots of CPUs
>    contending on a single file
>  - avoids the problems that Bruce found
>  - seems to work.
> 
> Thanks,
> NeilBrown
> 
> 
> ---
> 
> NeilBrown (9):
>       fs/locks: rename some lists and pointers.
>       fs/locks: split out __locks_wake_up_blocks().
>       NFS: use locks_copy_lock() to copy locks.
>       fs/locks: allow a lock request to block other requests.
>       fs/locks: always delete_block after waiting.
>       fs/locks: change all *_conflict() functions to return bool.
>       fs/locks: create a tree of dependent requests.
>       locks: merge posix_unblock_lock() and locks_delete_block()
>       VFS: locks: remove unnecessary white space.
> 
> 
>  fs/cifs/file.c                  |    4 -
>  fs/lockd/svclock.c              |    2 
>  fs/locks.c                      |  231 ++++++++++++++++++++++-----------------
>  fs/nfs/nfs4proc.c               |    6 +
>  fs/nfsd/nfs4state.c             |    6 +
>  include/linux/fs.h              |   11 +-
>  include/trace/events/filelock.h |   16 +--
>  7 files changed, 153 insertions(+), 123 deletions(-)
> 
> --
> Signature