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Subject: Re: [PATCH v4 00/34] Printbufs - new data structure for building
 strings
From:   Joe Perches <joe@perches.com>
To:     Kent Overstreet <kent.overstreet@gmail.com>
Cc:     David Laight <David.Laight@ACULAB.COM>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
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        "rostedt@goodmis.org" <rostedt@goodmis.org>,
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        "linux@rasmusvillemoes.dk" <linux@rasmusvillemoes.dk>,
        "willy@infradead.org" <willy@infradead.org>
Date:   Mon, 20 Jun 2022 18:26:58 -0700
In-Reply-To: <20220621005752.ohiq5besmy3r5rjo@moria.home.lan>
References: <20220620004233.3805-1-kent.overstreet@gmail.com>
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         <20220620150514.3tjy5dv7pv5frcwd@moria.home.lan>
         <53d77ae6101a0f24cfb694174d4c7699424c57e8.camel@perches.com>
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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.