linux-kernel - Re: [PATCH 0/5 - V2] locks: avoid thundering-herd wake-ups

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Date:   Thu, 9 Aug 2018 22:52:51 -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 0/5 - V2] locks: avoid thundering-herd wake-ups

On Fri, Aug 10, 2018 at 11:50:58AM +1000, NeilBrown wrote:
> You're good at this game!

Everybody's got to have a hobby, mine is pathological posix locking
cases....

> So, because a locker with the same "owner" gets a free pass, you can
> *never* say that any lock which conflicts with A also conflicts with B,
> as a lock with the same owner as B will never conflict with B, even
> though it conflicts with A.
> 
> I think there is still value in having the tree, but when a waiter is
> attached under a new blocker, we need to walk the whole tree beneath the
> waiter and detach/wake anything that is not blocked by the new blocker.

If you're walking the whole tree every time then it might as well be a
flat list, I think?

--b.