linux-kernel - Re: [PATCH] proc: calculate end pointer for /proc/*/* lookup at compile time

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Date:   Tue, 29 Jan 2019 14:18:48 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] proc: calculate end pointer for /proc/*/* lookup at
 compile time

On Mon, 14 Jan 2019 23:04:23 +0300 Alexey Dobriyan <adobriyan@...il.com> wrote:

> Compilers like to transform loops like
> 
> 	for (i = 0; i < n; i++) {
> 		[use p[i]]
> 	}
> 
> into
> 	for (p = p0; p < end; p++) {
> 		...
> 	}
> 
> Do it by hand, so that it results in overall simpler loop
> and smaller code.
> 
> Space savings:
> 
> 	$ ./scripts/bloat-o-meter ../vmlinux-001 ../obj/vmlinux
> 	add/remove: 0/0 grow/shrink: 2/1 up/down: 4/-9 (-5)
> 	Function                                     old     new   delta
> 	proc_tid_base_lookup                          17      19      +2
> 	proc_tgid_base_lookup                         17      19      +2
> 	proc_pident_lookup                           179     170      -9
> 
> Note: this trick bloats readdir, so don't do it :-\

I don't understand the Note:.  Can you please expand?