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

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Message-ID: <20170424130311.GR4021@tassilo.jf.intel.com>
Date:   Mon, 24 Apr 2017 06:03:11 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        "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

> Can you explain what the issue is?  What used to work on Linux and
> doesn't any more?  The man page is quite clear:

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.

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

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.

-Andi