linux-kernel - Re: [PATCH v2 0/6] kernfs: proposed locking and concurrency improvement

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Message-ID: <20200619222356.GA13061@mtj.duckdns.org>
Date:   Fri, 19 Jun 2020 18:23:56 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Rick Lindsley <ricklind@...ux.vnet.ibm.com>
Cc:     Ian Kent <raven@...maw.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/6] kernfs: proposed locking and concurrency
 improvement

On Fri, Jun 19, 2020 at 01:41:39PM -0700, Rick Lindsley wrote:
> On 6/19/20 8:38 AM, Tejun Heo wrote:
> 
> > I don't have strong objections to the series but the rationales don't seem
> > particularly strong. It's solving a suspected problem but only half way. It
> > isn't clear whether this can be the long term solution for the problem
> > machine and whether it will benefit anyone else in a meaningful way either.
> 
> I don't understand your statement about solving the problem halfway. Could
> you elaborate?

Spending 5 minutes during boot creating sysfs objects doesn't seem like a
particularly good solution and I don't know whether anyone else would
experience similar issues. Again, not necessarily against improving the
scalability of kernfs code but the use case seems a bit out there.

> > I think Greg already asked this but how are the 100,000+ memory objects
> > used? Is that justified in the first place?
> 
> They are used for hotplugging and partitioning memory. The size of the
> segments (and thus the number of them) is dictated by the underlying
> hardware.

This sounds so bad. There gotta be a better interface for that, right?

Thanks.

-- 
tejun