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Date: Wed, 2 May 2018 17:52:23 -0700
From: Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH v4 07/16] slub: Remove page->counters
Message-ID: <20180503005223.GB21199@bombadil.infradead.org>
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To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Christopher Lameter <cl@linux.com>, linux-mm@kvack.org, Matthew Wilcox <mawilcox@microsoft.com>, Andrew Morton <akpm@linux-foundation.org>, Lai Jiangshan <jiangshanlai@gmail.com>, Pekka Enberg <penberg@kernel.org>, Vlastimil Babka <vbabka@suse.cz>, Dave Hansen <dave.hansen@linux.intel.com>, =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>

On Thu, May 03, 2018 at 01:17:02AM +0300, Kirill A. Shutemov wrote:
> On Wed, May 02, 2018 at 05:26:39PM +0000, Matthew Wilcox wrote:
> > Option 2:
> > +                       union {
> > +                               unsigned long counters;
> > +                               struct {
> > +                                       unsigned inuse:16;
> > +                                       unsigned objects:15;
> > +                                       unsigned frozen:1;
> > +                               };
> > +                       };
> > 
> > Pro: Expresses exactly what we do.
> > Con: Back to five levels of indentation in struct page
> 
> The indentation issue can be fixed (to some extend) by declaring the union
> outside struct page and just use it inside.
> 
> I don't advocate for the approach, just listing the option.

Actually, you can't have an anonymous tagged union without -fms-extensions
(which got zero comments when I proposed it to lkml) or -fplan9-extensions
(which would require gcc 4.6)