linux-kernel - Re: [PATCH 10/18] fsinfo: Provide notification overrun handling support [ver #21]

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Date:   Wed, 05 Aug 2020 10:05:36 +0800
From:   Ian Kent <raven@...maw.net>
To:     Miklos Szeredi <miklos@...redi.hu>,
        David Howells <dhowells@...hat.com>
Cc:     viro@...iv.linux.org.uk, torvalds@...ux-foundation.org,
        mszeredi@...hat.com, christian@...uner.io, jannh@...gle.com,
        darrick.wong@...cle.com, kzak@...hat.com, jlayton@...hat.com,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/18] fsinfo: Provide notification overrun handling
 support [ver #21]

On Tue, 2020-08-04 at 15:56 +0200, Miklos Szeredi wrote:
> On Mon, Aug 03, 2020 at 02:37:50PM +0100, David Howells wrote:
> > Provide support for the handling of an overrun in a watch
> > queue.  In the
> > event that an overrun occurs, the watcher needs to be able to find
> > out what
> > it was that they missed.  To this end, previous patches added event
> > counters to struct mount.
> 
> So this is optimizing the buffer overrun case?
> 
> Shoun't we just make sure that the likelyhood of overruns is low and
> if it
> happens, just reinitialize everthing from scratch (shouldn't be
> *that*
> expensive).

But maybe not possible if you are using notifications for tracking
state in user space, you need to know when the thing you have needs
to be synced because you missed something and it's during the
notification processing you actually have the object that may need
to be refreshed.

> 
> Trying to find out what was missed seems like just adding complexity
> for no good
> reason.
>