linux-kernel - Re: [PATCH v4 00/34] Printbufs - new data structure for building strings

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Message-ID: <20220621005752.ohiq5besmy3r5rjo@moria.home.lan>
Date:   Mon, 20 Jun 2022 20:57:52 -0400
From:   Kent Overstreet <kent.overstreet@...il.com>
To:     Joe Perches <joe@...ches.com>
Cc:     David Laight <David.Laight@...LAB.COM>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "pmladek@...e.com" <pmladek@...e.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "enozhatsky@...omium.org" <enozhatsky@...omium.org>,
        "linux@...musvillemoes.dk" <linux@...musvillemoes.dk>,
        "willy@...radead.org" <willy@...radead.org>
Subject: Re: [PATCH v4 00/34] Printbufs - new data structure for building
 strings

On Mon, Jun 20, 2022 at 05:38:51PM -0700, Joe Perches wrote:
> On Mon, 2022-06-20 at 11:07 -0400, Kent Overstreet wrote:
> > On Mon, Jun 20, 2022 at 04:19:31AM +0000, David Laight wrote:
> > > I really think that is a bad idea.
> > > printk() already uses a lot of stack, anything doing a recursive
> > > call is just making that worse.
> > > Especially since these calls can often be in error paths
> > > which are not often tested and can already be on deep stacks.
> > 
> > We went over this before - this patch series drastically reduces stack usage of
> > sprintf by eliminating a bunch of stack allocated buffers. Do try to keep up...
> 
> I generally agree with David.
> 
> I think Kent has not provided data that this actually _reduces_
> stack usage.

I think the people who are comfortable with reading C can discern that when
large stack allocated character arrays are deleted, frame size and stack usage
go down.