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Date:   Fri, 23 Mar 2018 13:06:20 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Baoquan He <bhe@redhat.com>
Cc:     linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
        takahiro.akashi@linaro.org, ebiederm@xmission.com,
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Subject: Re: [PATCH 1/2] resource: add walk_system_ram_res_rev()
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On Fri, 23 Mar 2018 11:10:13 +0800 Baoquan He <bhe@redhat.com> wrote:

> On 03/22/18 at 07:06pm, Andrew Morton wrote:
> > On Fri, 23 Mar 2018 08:58:45 +0800 Baoquan He <bhe@redhat.com> wrote:
> > 
> > > > erk, this is pretty nasty.  Isn't there a better way :(
> > > 
> > > Yes, this is not efficient.
> > > 
> > > In struct resource{}, ->sibling list is a singly linked list. I ever
> > > thought about changing it to doubly linked list, yet not very sure if
> > > it will have effect since struct resource is a core data structure.
> > 
> > Switching to a list_head sounds OK.  The only issue really is memory
> > consumption and surely we don't have tens of thousands of struct
> > resources floating about(?).  Or if we do have a lot, the machine is
> > presumably huge (hope?).
> 
> Yes. It doubles the memory consumption.
> 
> AFAIK, the biggest number of resrouces I heard of possibly is mentioned
> in this user space kexec_tools commit. In this commit, Xunlei told on
> SGI system with 64TB RAM, the array which we have been using to store
> "System RAM"|"Reserved"|"ACPI **" regions is not big enough. In that
> case, we need extra 8Byte*2048=16KB at most. With my understanding, this
> increase is system wide, since each resource instance only needs its own
> list_head member, right?

Yes.  That sounds perfectly acceptable.

It would be interesting to see what this approach looks like, if you
have time to toss something together?