linux-kernel - Re: [PATCH -mm] procfs: add VmFlags field in smaps output v3

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Date:	Thu, 25 Oct 2012 00:41:13 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH -mm] procfs: add VmFlags field in smaps output v3

On Wed, Oct 24, 2012 at 01:36:52PM -0700, Andrew Morton wrote:
> > ...
> >
> > +	for_each_set_bit(i, &vma->vm_flags, BITS_PER_LONG) {
> 
> for_each_set_bit() seems to be rather sucky.  Going back to 
> 
> --- a/fs/proc/task_mmu.c~a-fix
> +++ a/fs/proc/task_mmu.c
> @@ -568,10 +568,11 @@ static void show_smap_vma_flags(struct s
>  	size_t i;
>  
>  	seq_puts(m, "VmFlags: ");
> -	for_each_set_bit(i, &vma->vm_flags, BITS_PER_LONG) {
> -		seq_printf(m, "%c%c ",
> -			   mnemonics[i][0],
> -			   mnemonics[i][1]);
> +	for (i = 0; i < BITS_PER_LONG; i++) {
> +		if (vma->vm_flags & (1UL << i)) {
> +			seq_printf(m, "%c%c ",
> +				   mnemonics[i][0], mnemonics[i][1]);
> +		}
>  	}
>  	seq_putc(m, '\n');
>  }
> 
> saves 41 bytes.  That's rather a lot for such a small code sequence.

OK, bits-per-long is not a big value here, neither the function is time
critical one, so thanks!
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