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

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Message-ID: <20220621023145.sx3o3txbmbsa3br6@moria.home.lan>
Date:   Mon, 20 Jun 2022 22:31:45 -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 06:26:58PM -0700, Joe Perches wrote:
> On Mon, 2022-06-20 at 20:57 -0400, Kent Overstreet wrote:
> > 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.
> 
> I am very comfortable reading C.
> 
> You have not provided any data.

It seems like neither of you have even bothered to check stack frame size in the
current code, and you guys are the one asserting that this is an issue.