linux-kernel - Re: file metadata via fs API

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Message-ID: <d2d179c7-9b60-ca1a-0c9f-d308fc7af5ce@redhat.com>
Date:   Wed, 12 Aug 2020 10:43:24 +0100
From:   Steven Whitehouse <swhiteho@...hat.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     David Howells <dhowells@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>, Karel Zak <kzak@...hat.com>,
        Jeff Layton <jlayton@...hat.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Christian Brauner <christian@...uner.io>,
        Lennart Poettering <lennart@...ttering.net>,
        Linux API <linux-api@...r.kernel.org>,
        Ian Kent <raven@...maw.net>,
        LSM <linux-security-module@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: file metadata via fs API

Hi,

On 12/08/2020 09:37, Miklos Szeredi wrote:
[snip]
>
> b) The awarded performance boost is not warranted for the use cases it
> is designed for.
>
> Thanks,
> Miklos
>

This is a key point. One of the main drivers for this work is the 
efficiency improvement for large numbers of mounts. Ian and Karel have 
already provided performance measurements showing a significant benefit 
compared with what we have today. If you want to propose this 
alternative interface then you need to show that it can sustain similar 
levels of performance, otherwise it doesn't solve the problem. So 
performance numbers here would be helpful.

Also - I may have missed this earlier in the discussion, what are the 
atomicity guarantees with this proposal? This is the other key point for 
the API, so it would be good to see that clearly stated (i.e. how does 
one use it in combination with the notifications to provide an up to 
date, consistent view of the kernel's mounts)

Steve.