linux-kernel - Re: [rfc 0/2] Introducing VmFlags field into smaps output

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Date:	Tue, 23 Oct 2012 10:13:41 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Pavel Emelyanov <xemul@...allels.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [rfc 0/2] Introducing VmFlags field into smaps output

On Mon, Oct 22, 2012 at 02:51:58PM -0700, Andrew Morton wrote:
...
> > +	__seq_show_vmflag(VM_DONTEXPAND,"de ");
> > +	__seq_show_vmflag(VM_ACCOUNT,	"ac ");
> > +	__seq_show_vmflag(VM_NORESERVE,	"nr ");
> > +	__seq_show_vmflag(VM_HUGETLB,	"ht ");
> > +	__seq_show_vmflag(VM_NONLINEAR,	"nl ");
> > +	__seq_show_vmflag(VM_ARCH_1,	"ar ");
> > +	__seq_show_vmflag(VM_DONTDUMP,	"dd ");
> > +	__seq_show_vmflag(VM_MIXEDMAP,	"mm ");
> > +	__seq_show_vmflag(VM_HUGEPAGE,	"hg ");
> > +	__seq_show_vmflag(VM_NOHUGEPAGE,"nh ");
...
> 
> This code would be much denser if we did the old
> 
> 	static const char foo[] = "rdwrexshmrmw...";
> 	unsigned i;
> 
> 	for (i = 0; i < BITS_PER_LONG; i++) {
> 		if (flags & (1 << i))
> 			seq_printf("%c%c ", foo[i * 2], foo[i * 2 + 1]);
> 	}
> 
> trick.  But then we'd have to remember to fix foo[] each time we
> alter the flags, so maybe let's not do that.

Yup, but not only that, this kind of trick hides associativity between
VM_ constant and mnemonic, so on changes one would have to figure out
which position some flag has in this foo[] array, so I vote for not
use it :-)
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