linux-kernel - Re: [PATCHv3 1/2] mm/memblock: extend the limit inferior of bottom-up after parsing hotplug attr

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Message-ID: <CAFgQCTt2=6mwFid8HS+K5UsqkBv8y7N5WOoKpVxYzNxjwmV75A@mail.gmail.com>
Date:   Mon, 7 Jan 2019 16:37:54 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Mike Rapoport <rppt@...ux.ibm.com>, Baoquan He <bhe@...hat.com>,
        linux-acpi@...r.kernel.org, linux-mm@...ck.org,
        kexec@...ts.infradead.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Michal Hocko <mhocko@...e.com>,
        Jonathan Corbet <corbet@....net>,
        Yaowei Bai <baiyaowei@...s.chinamobile.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Daniel Vacek <neelx@...hat.com>,
        Mathieu Malaterre <malat@...ian.org>,
        Stefan Agner <stefan@...er.ch>, Dave Young <dyoung@...hat.com>,
        yinghai@...nel.org, vgoyal@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 1/2] mm/memblock: extend the limit inferior of bottom-up
 after parsing hotplug attr

I send out a series [RFC PATCH 0/4] x86_64/mm: remove bottom-up
allocation style by pushing forward the parsing of mem hotplug info (
https://lore.kernel.org/lkml/1546849485-27933-1-git-send-email-kernelfans@gmail.com/T/#t).
Please give comment if you are interested.

Thanks,
Pingfan

On Fri, Jan 4, 2019 at 2:47 AM Tejun Heo <tj@...nel.org> wrote:
>
> Hello,
>
> On Wed, Jan 02, 2019 at 07:05:38PM +0200, Mike Rapoport wrote:
> > I agree that currently the bottom-up allocation after the kernel text has
> > issues with KASLR. But this issues are not necessarily related to the
> > memory hotplug. Even with a single memory node, a bottom-up allocation will
> > fail if KASLR would put the kernel near the end of node0.
> >
> > What I am trying to understand is whether there is a fundamental reason to
> > prevent allocations from [0, kernel_start)?
> >
> > Maybe Tejun can recall why he suggested to start bottom-up allocations from
> > kernel_end.
>
> That's from 79442ed189ac ("mm/memblock.c: introduce bottom-up
> allocation mode").  I wasn't involved in that patch, so no idea why
> the restrictions were added, but FWIW it doesn't seem necessary to me.
>
> Thanks.
>
> --
> tejun