linux-kernel - Re: [RFC 4/9] gfs2: Fix mmap + page fault deadlocks (part 1)

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Message-ID: <YMUokdiLMIpr8ee/@zeniv-ca.linux.org.uk>
Date:   Sat, 12 Jun 2021 21:35:13 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Andreas Gruenbacher <agruenba@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        cluster-devel <cluster-devel@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jan Kara <jack@...e.cz>, Matthew Wilcox <willy@...radead.org>
Subject: Re: [RFC 4/9] gfs2: Fix mmap + page fault deadlocks (part 1)

On Sat, Jun 12, 2021 at 09:05:40PM +0000, Al Viro wrote:

> Is the above an accurate description of the mainline situation there?
> In particular, normal read doesn't seem to bother with locks at all.
> What exactly are those cluster locks for in O_DIRECT read?

BTW, assuming the lack of contention, how costly is dropping/regaining
such cluster lock?