linux-kernel - Re: [PATCH] x86, mm: Reserver some memory for bootmem allocator for NO

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Message-ID: <20180830124915.GH2656@dhcp22.suse.cz>
Date:   Thu, 30 Aug 2018 14:49:15 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Feng Tang <feng.tang@...el.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Ingo Molnar <mingo@...e.hu>,
        "H . Peter Anvin" <hpa@...ux.intel.com>,
        Yinghai Lu <yinghai@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH] x86, mm: Reserver some memory for bootmem allocator for
 NO_BOOTMEM

On Thu 30-08-18 13:54:19, Thomas Gleixner wrote:
> On Thu, 30 Aug 2018, Michal Hocko wrote:
> > On Thu 30-08-18 12:44:02, Peter Zijlstra wrote:
> > > On Thu, Aug 30, 2018 at 05:03:19PM +0800, Feng Tang wrote:
> > > > The root cause is that when CONFIG_NO_BOOTMEM=y,  before
> > > > e820__memblock_setup() is called there is no memory for bootmem
> > > > to allocate,
> > > 
> > > Which you bloody well asked for by using NO_BOOTMEM=y.
> > > 
> > > Going down this route; adding hacks for every little thing that does
> > > want bootmem, completely defeats the purpose.
> > > 
> > > If anything, make the earlycon thing depend on NO_BOOTMEM=n. That also
> > > solves your problem. No earlycon, no panic.
> > 
> > Well, there is endeavor to remove bootmem allocator altogether. So
> > making earlycon depend on NO_BOOTMEM=n doesn't sound like a good fit to
> 
> If we want to remove bootmem, then reintroducing it with a static bootmem
> section doesn't make any sense at all.

I have actually checked the code now and see what you mean. I thought it
would be a single allocation that is needed but that is not the case so
the static buffer is not going to fly.
-- 
Michal Hocko
SUSE Labs