linux-kernel - Re: [PATCH RFC] fs,ipc: batch RCU synchronization in free

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Date:   Mon, 15 Aug 2022 21:05:18 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     linux-kernel@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Alexey Gladkov <legion@...nel.org>, linux-fs@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH RFC] fs,ipc: batch RCU synchronization in free_ipc

On Mon, 2022-08-15 at 22:40 +0100, Al Viro wrote:
> On Mon, Aug 15, 2022 at 05:26:20PM -0400, Rik van Riel wrote:
> > TL;DR: it runs better than it looks, and I am looking for ideas on
> > how to make it look better
> 
> > Unfortunately there seems to be a tradeoff between temporarily
> > allocating things on the stack, and having slightly uglier code,
> > or adding a struct rcu_work to the struct vfsmount.
> > 
> > I am not entirely happy with the way this code looks, and hoping
> > for suggestions on how to improve it.
> > 
> 
> IMO you are going in wrong direction with that; it's a long story,
> and I've partial writeup on that, but I won't have it ready for
> posting until the end of the week.  Put it that way - there's
> a possibility of reorganizing the way mount refcounts work,
> eliminating this synchronize_rcu().  RCU delay still has to happen
> in some form, but we get smarter ways to wait for it.
> 
I'm more than happy to abandon this approach.

I looked at this a bunch, and could not find a
nice way to do this the way the VFS currently
works, and am looking forward to getting this
done in a better way!


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