linux-kernel - Re: [RFC PATCH] getvalues(2) prototype

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Message-ID: <YjrIvRCg2iUeMN2V@kroah.com>
Date:   Wed, 23 Mar 2022 08:14:05 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     Miklos Szeredi <mszeredi@...hat.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-man@...r.kernel.org,
        linux-security-module@...r.kernel.org, Karel Zak <kzak@...hat.com>,
        Ian Kent <raven@...maw.net>,
        David Howells <dhowells@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <christian@...uner.io>,
        Amir Goldstein <amir73il@...il.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>
Subject: Re: [RFC PATCH] getvalues(2) prototype

On Tue, Mar 22, 2022 at 01:36:26PM -0700, Casey Schaufler wrote:
> On 3/22/2022 12:27 PM, Miklos Szeredi wrote:
> > Add a new userspace API that allows getting multiple short values in a
> > single syscall.
> > 
> > This would be useful for the following reasons:
> > 
> > - Calling open/read/close for many small files is inefficient.  E.g. on my
> >    desktop invoking lsof(1) results in ~60k open + read + close calls under
> >    /proc and 90% of those are 128 bytes or less.
> 
> You don't need the generality below to address this issue.
> 
> int openandread(const char *path, char *buffer, size_t size);
> 
> would address this case swimmingly.

Or you can use my readfile(2) proposal:
	https://lore.kernel.org/r/20200704140250.423345-1-gregkh@linuxfoundation.org

But you had better actually benchmark the thing.  Turns out that I could
not find a real-world use that shows improvements in anything.

Miklos, what userspace tool will use this new syscall and how will it be
faster than readfile() was?

I should rebase that against 5.17 again and see if anything is different
due to the new spectre-bhb slowdowns.

thanks,

greg k-h