Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64

From	Will Deacon <will.deacon@arm.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64
Date	2016-04-11 12:50 +0200
Message-ID	<rmHzQ-4kX-3@gated-at.bofh.it> (permalink)
References	(3 earlier) <rmEBY-26A-7@gated-at.bofh.it> <rmEVl-2eN-15@gated-at.bofh.it> <rmF50-2CR-13@gated-at.bofh.it> <rmGX8-3Zo-9@gated-at.bofh.it> <rmHqa-4eH-19@gated-at.bofh.it>
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On Mon, Apr 11, 2016 at 12:31:53PM +0200, Ard Biesheuvel wrote:
> On 11 April 2016 at 11:59, Chen Feng <puck.chen@hisilicon.com> wrote:
> > Please see the pg-tables below.
> >
> >
> > With sparse and vmemmap enable.
> >
> > ---[ vmemmap start ]---
> > 0xffffffbdc0200000-0xffffffbdc4800000          70M     RW NX SHD AF    UXN MEM/NORMAL
> > ---[ vmemmap end ]---
> >
> 
> OK, I see what you mean now. Sorry for taking so long to catch up.
> 
> > The board is 4GB, and the memap is 70MB
> > 1G memory --- 14MB mem_map array.
> 
> No, this is incorrect. 1 GB corresponds with 16 MB worth of struct
> pages assuming sizeof(struct page) == 64
> 
> So you are losing 6 MB to rounding here, which I agree is significant.
> I wonder if it makes sense to use a lower value for SECTION_SIZE_BITS
> on 4k pages kernels, but perhaps we're better off asking the opinion
> of the other cc'ees.

You need to be really careful making SECTION_SIZE_BITS smaller because
it has a direct correlation on the use of page->flags and you can end up
running out of bits fairly easily.

Will

Thread

[PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Chen Feng <puck.chen@hisilicon.com> - 2016-04-05 10:30 +0200
  Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Chen Feng <puck.chen@hisilicon.com> - 2016-04-07 09:50 +0200
  Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Will Deacon <will.deacon@arm.com> - 2016-04-07 16:30 +0200
    Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Chen Feng <puck.chen@hisilicon.com> - 2016-04-11 05:00 +0200
      Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2016-04-11 09:40 +0200
        Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Chen Feng <puck.chen@hisilicon.com> - 2016-04-11 10:00 +0200
          Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2016-04-11 10:10 +0200
            Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Chen Feng <puck.chen@hisilicon.com> - 2016-04-11 12:10 +0200
              Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2016-04-11 12:40 +0200
                Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Will Deacon <will.deacon@arm.com> - 2016-04-11 12:50 +0200
                Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Chen Feng <puck.chen@hisilicon.com> - 2016-04-11 13:00 +0200
                Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Laura Abbott <labbott@redhat.com> - 2016-04-11 20:20 +0200
                Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Catalin Marinas <catalin.marinas@arm.com> - 2016-04-12 16:50 +0200
                Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Catalin Marinas <catalin.marinas@arm.com> - 2016-04-12 17:00 +0200
              Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Chen Feng <puck.chen@hisilicon.com> - 2016-04-11 12:50 +0200
                Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2016-04-11 13:10 +0200
      Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Jungseok Lee <jungseoklee85@gmail.com> - 2016-04-12 16:10 +0200

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