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References: <1284092586-1179-1-git-send-email-n-horiguchi@ah.jp.nec.com>
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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 10 Sep 2010 15:07:08 -0700
Message-ID: <AANLkTinFqM4BSD0jkrqkrNxg-o+3eC6QQ6zq8jKdaLJx@mail.gmail.com>
Subject: Re: [PATCH 1/4] hugetlb, rmap: always use anon_vma root pointer
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Sender: owner-linux-mm@kvack.org
To: Andi Kleen <andi@firstfloor.org>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, LKML <linux-kernel@vger.kernel.org>, Andrea Arcangeli <aarcange@redhat.com>, Hugh Dickins <hughd@google.com>, Christoph Lameter <cl@linux.com>, Andrew Morton <akpm@linux-foundation.org>, Rik van Riel <riel@redhat.com>, Peter Zijlstra <peterz@infradead.org>, linux-mm <linux-mm@kvack.org>
List-ID: <linux-mm.kvack.org>

On Fri, Sep 10, 2010 at 2:50 PM, Andi Kleen <andi@firstfloor.org> wrote:
>> Btw, why isn't the code in __page_set_anon_rmap() also doing this
>> cleaner version (ie a single "if (PageAnon(page)) return;" up front)?
>
> Perhaps I misunderstand the question, but __page_set_anon_rmap
> should handle Anon pages, shouldn't it?

I'm talking about this:

    if (!exclusive) {
        if (PageAnon(page))
            return;
        anon_vma = anon_vma->root;
    } else {
        .. big bad comment ...
        if (PageAnon(page))
            return;
    }

where both sides of the if-statement start off doing the same thing.

It would be much cleaner to just do

    ... big _comprehensible_ comment ...
    if (PageAnon(page))
        return;

    if (!exclusive)
        anon_vma = anon_vma->root;

which avoids that silly else that just does something that we always do.

The reason I reacted is that Naoya-san's patch did that cleaner
version for the hugetlb case. So when I compared it to the non-hugetlb
case I just went "Ewww..."

                             Linus

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