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

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Date:   Mon, 20 Jun 2022 17:38:51 -0700
From:   Joe Perches <joe@...ches.com>
To:     Kent Overstreet <kent.overstreet@...il.com>,
        David Laight <David.Laight@...LAB.COM>
Cc:     "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, 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.

Converting stack variables to call stack frames does not necessarily
reduce overall stack usage when the stack frame plus any locally
used stack in the called function is added together.