linux-kernel - Re: [RFC/RFT PATCH 1/3] memblock: update initialization of reserved pages

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Message-ID: <1065c0ac-f9e3-2d3a-1ec4-a5c28f98c6ae@redhat.com>
Date:   Fri, 16 Apr 2021 13:54:00 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        kvmarm <kvmarm@...ts.cs.columbia.edu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [RFC/RFT PATCH 1/3] memblock: update initialization of reserved
 pages

On 16.04.21 13:44, Mike Rapoport wrote:
> On Thu, Apr 15, 2021 at 11:30:12AM +0200, David Hildenbrand wrote:
>>> Not sure we really need a new pagetype here, PG_Reserved seems to be quite
>>> enough to say "don't touch this".  I generally agree that we could make
>>> PG_Reserved a PageType and then have several sub-types for reserved memory.
>>> This definitely will add clarity but I'm not sure that this justifies
>>> amount of churn and effort required to audit uses of PageResrved().
>>>> Then, we could mostly avoid having to query memblock at runtime to figure
>>>> out that this is special memory. This would obviously be an extension to
>>>> this series. Just a thought.
>>>
>>> Stop pushing memblock out of kernel! ;-)
>>
>> Can't stop. Won't stop. :D
>>
>> It's lovely for booting up a kernel until we have other data-structures in
>> place ;)
> 
> A bit more seriously, we don't have any data structure that reliably
> represents physical memory layout and arch-independent fashion.
> memblock is probably the best starting point for eventually having one.

We have the (slowish) kernel resource tree after boot and the (faster) 
memmap. I really don't see why we really need another slowish variant.

We might be better off to just extend and speed up the kernel resource tree.

Memblock as is is not a reasonable datastructure to keep around after 
boot: for example, how we handle boottime allocations and reserve 
regions both as reserved.

-- 
Thanks,

David / dhildenb