linux-kernel - Re: [PATCH] kexec: allocate buffer in top-down, if specified, correctly

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Date:   Fri, 28 Apr 2017 16:33:34 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
To:     AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:     dyoung@...hat.com, bhe@...hat.com, vgoyal@...hat.com,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kexec: allocate buffer in top-down, if specified, correctly

Am Freitag, 28. April 2017, 09:51:39 BRT schrieb AKASHI Takahiro:
> On Thu, Apr 27, 2017 at 07:00:04PM -0300, Thiago Jung Bauermann wrote:
> > Hello,
> > 
> > Am Mittwoch, 26. April 2017, 17:22:09 BRT schrieb AKASHI Takahiro:
> > > The current kexec_locate_mem_hole(kbuf.top_down == 1) stops searching at
> > > the first memory region that has enough space for requested size even if
> > > some of higher regions may also have.
> > 
> > kexec_locate_mem_hole expects arch_kexec_walk_mem to walk memory from top
> > to bottom if top_down is true. That is what powerpc's version does.
> 
> Ah, I haven't noticed that, but x86 doesn't have arch_kexec_walk_mem and
> how can it work for x86?

Looking at v4.9's kexec_add_buffer, the logic has been this way before I 
factored kexec_locate_mem_hole out of it. So x86 has been behaving this way 
for a while.

> > Isn't it possible to walk resources from top to bottom?
> 
> Yes, it will be, but it seems to me that such a behavior is not intuitive
> and even confusing if it doesn't come with explicit explanation.

Yes, I should have put a comment pointing out that assumption.

-- 
Thiago Jung Bauermann
IBM Linux Technology Center