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Message-ID: <84144f020805072227i3382465eleccded79d9fcf532@mail.gmail.com>
Date: Thu, 8 May 2008 08:27:47 +0300
From: "Pekka Enberg" <penberg@cs.helsinki.fi>
To: "Andrea Arcangeli" <andrea@qumranet.com>
Subject: Re: [PATCH 08 of 11] anon-vma-rwsem
Cc: "Linus Torvalds" <torvalds@linux-foundation.org>,
       "Christoph Lameter" <clameter@sgi.com>,
       "Andrew Morton" <akpm@linux-foundation.org>, steiner@sgi.com,
       holt@sgi.com, npiggin@suse.de, a.p.zijlstra@chello.nl,
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On Thu, May 8, 2008 at 8:20 AM, Andrea Arcangeli <andrea@qumranet.com> wrote:
>  Actually I looked both at the struct and at the slab alignment just in
>  case it was changed recently. Now after reading your mail I also
>  compiled it just in case.
>
>  @@ -27,6 +27,7 @@ struct anon_vma {
>   struct anon_vma {
>
>         spinlock_t lock;        /* Serialize access to vma list */
>
>         struct list_head head;  /* List of private "related" vmas */
>  +       int flag:1;
>   };

You might want to read carefully what Linus wrote:

> The one that already has a 4 byte padding thing on x86-64 just after the
> spinlock? And that on 32-bit x86 (with less than 256 CPU's) would have two
> bytes of padding if we didn't just make the spinlock type unconditionally
> 32 bits rather than the 16 bits we actually _use_?

So you need to add the flag _after_ ->lock and _before_ ->head....

                        Pekka