linux-kernel - Re: [PATCH 1/4] hugetlb, rmap: always use anon

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Message-ID: <AANLkTinFqM4BSD0jkrqkrNxg-o+3eC6QQ6zq8jKdaLJx@mail.gmail.com>
Date:	Fri, 10 Sep 2010 15:07:08 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Lameter <cl@...ux.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH 1/4] hugetlb, rmap: always use anon_vma root pointer

On Fri, Sep 10, 2010 at 2:50 PM, Andi Kleen <andi@...stfloor.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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