linux-kernel - Re: Question on the five-level page table support patches

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Message-ID: <8f8467b5-70e6-466b-f53b-1c64622ba82d@physik.fu-berlin.de>
Date:   Mon, 24 Apr 2017 22:33:22 +0200
From:   John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To:     Andi Kleen <ak@...ux.intel.com>, Andy Lutomirski <luto@...nel.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Michal Hocko <mhocko@...e.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: Question on the five-level page table support patches

On 04/24/2017 03:03 PM, Andi Kleen wrote:
> In old Linux hint was a search hint, so if there isn't a hole
> at the hinted area it will search starting from there for a hole
> instead of giving up immediately.

Yep, that's what I meant. It used to work like that and it still
works like that on NetBSD, for example. Although it has apparently
been a long time since it changed [1].

> Now it just gives up, which means every user has to implement
> their own search.

Correct. And the resulting code is usually ugly and inefficient [2].

> Yes I ran into the same problem and it's annoying. It broke
> originally when top down mmap was added I believe
> 
> Before the augmented rbtree it was potentially very expensive, but now
> it should be cheap.

I'm not sure whether I understand what that means.

Thanks,
Adrian

> [1] http://lkml.iu.edu/hypermail/linux/kernel/0305.2/0828.html
> [2] https://hg.mozilla.org/mozilla-central/rev/dfaafbaaa291

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaubitz@...ian.org
`. `'   Freie Universitaet Berlin - glaubitz@...sik.fu-berlin.de
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