linux-kernel - Re: [PATCH 1/2] resource: add walk_system_ram_res

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Message-ID: <20180324133330.GD25740@localhost.localdomain>
Date:   Sat, 24 Mar 2018 21:33:30 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     prudo@...ux.vnet.ibm.com, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org, takahiro.akashi@...aro.org,
        ebiederm@...ssion.com, dyoung@...hat.com, vgoyal@...hat.com
Subject: Re: [PATCH 1/2] resource: add walk_system_ram_res_rev()

On 03/23/18 at 01:06pm, Andrew Morton wrote:
> On Fri, 23 Mar 2018 11:10:13 +0800 Baoquan He <bhe@...hat.com> wrote:
> 
> > On 03/22/18 at 07:06pm, Andrew Morton wrote:
> > > On Fri, 23 Mar 2018 08:58:45 +0800 Baoquan He <bhe@...hat.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?

OK, will make patches for reviewing. Thanks!