Re: [PATCH 1/1] riscv: select CONFIG_ARCH_KEEP_MEMBLOCK

From: Palmer Dabbelt
Date: Sat Sep 11 2021 - 02:47:03 EST

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On Mon, 16 Aug 2021 11:50:26 PDT (-0700), rppt@xxxxxxxxxx wrote:

Hi Heinrich,

On Mon, Aug 16, 2021 at 05:52:11PM +0200, Heinrich Schuchardt wrote:

On 8/16/21 5:30 PM, Kefeng Wang wrote:
>
> On 2021/8/16 22:47, Heinrich Schuchardt wrote:
> > For analyzing memory blocks we can either use the memblock=debug command
> > line argument which creates massive output or a debug file system.
> >
> > Select CONFIG_ARCH_KEEP_MEMBLOCK to provide a debugfs at
> > /sys/kernel/debug/memblock to analyze memory blocks. The
> > same is already done for arm, arm64, mips, powerpc.
> >
> > The actual provisioning of the file system depends on CONFIG_DEBUG_FS.
>
> Hi，for riscv, it don't use memblock(eg, no provide pfn_valid to use
> memblock),
>
> we could call memblock_discard() to discard memblock private memory to save
>
> some memory, right? So I think we don't need this config for now.

What do you mean by "it don't use memblock?

If you boot the HiFive Unmatched with memblock=debug you will see output
like the one below. This is the information that you can see in the debug
file system if CONFIG_DEBUG_FS and CONFIG_ARCH_KEEP_MEMBLOCK will be
enabled.

Indeed having this info in debugfs is more convenient, but it comes with a
cost of several kilobytes of code and data for *every* riscv build.

Why parsing "memblock=debug" output is not enough?
What is the use-case that justifies the costs associated with having the
debugfs entries?

If someone can provide a use case I'm happy to look at how to enable it. Otherwise I think we should just stick with the standard way of doing things, which according to 350e88bad496 ("mm: memblock: make keeping memblock memory opt-in rather than opt-out") seems to be that ARCH_KEEP_MEMBLOCK is for ports that need that information, not just those that pass it through to userspace.

[ 0.000000] MEMBLOCK configuration:
[ 0.000000] memory size = 0x00000003ffe00000 reserved size =
0x000000001290fb70
[ 0.000000] memory.cnt = 0x25

BTW, it seems that the memory allocation by firmware is, well, suboptimal
and begs for fixes. I don't see why all these NOMAP areas cannot be put in
one contiguous chunk. I doubt they need to be NOMAP at all, but mysterious
the ways of ACPI.

We talked about this a bit in IRC and another thread, but it looks like this mess has ended up in the specs. From my reading that was likely the result of a blind copy/paste from some other architecture, but it's in a released spec so it's cannon and I'm not really interested in trying to change it as I'm tired of getting yelled at by the foundation folks.

[ 0.000000] memory[0x0] [0x0000000080200000-0x00000000fe6e2fff],
0x000000007e4e3000 bytes flags: 0x0
[ 0.000000] memory[0x1] [0x00000000fe6e3000-0x00000000fe6e5fff],
0x0000000000003000 bytes flags: 0x4
[ 0.000000] memory[0x2] [0x00000000fe6e6000-0x00000000fe709fff],
0x0000000000024000 bytes flags: 0x0
[ 0.000000] memory[0x3] [0x00000000fe70a000-0x00000000fe70bfff],
0x0000000000002000 bytes flags: 0x4
[ 0.000000] memory[0x4] [0x00000000fe70c000-0x00000000fe70ffff],
0x0000000000004000 bytes flags: 0x0
[ 0.000000] memory[0x5] [0x00000000fe710000-0x00000000fe710fff],
0x0000000000001000 bytes flags: 0x4
[ 0.000000] memory[0x6] [0x00000000fe711000-0x00000000fe712fff],
0x0000000000002000 bytes flags: 0x0
[ 0.000000] memory[0x7] [0x00000000fe713000-0x00000000fe716fff],
0x0000000000004000 bytes flags: 0x4
[ 0.000000] memory[0x8] [0x00000000fe717000-0x00000000fe717fff],
0x0000000000001000 bytes flags: 0x0
[ 0.000000] memory[0x9] [0x00000000fe718000-0x00000000fe71cfff],
0x0000000000005000 bytes flags: 0x4
[ 0.000000] memory[0xa] [0x00000000fe71d000-0x00000000fe71dfff],
0x0000000000001000 bytes flags: 0x0
[ 0.000000] memory[0xb] [0x00000000fe71e000-0x00000000fe71efff],
0x0000000000001000 bytes flags: 0x4
[ 0.000000] memory[0xc] [0x00000000fe71f000-0x00000000fe71ffff],
0x0000000000001000 bytes flags: 0x0
[ 0.000000] memory[0xd] [0x00000000fe720000-0x00000000fe720fff],
0x0000000000001000 bytes flags: 0x4
[ 0.000000] memory[0xe] [0x00000000fe721000-0x00000000fe721fff],
0x0000000000001000 bytes flags: 0x0
[ 0.000000] memory[0xf] [0x00000000fe722000-0x00000000fe722fff],
0x0000000000001000 bytes flags: 0x4
[ 0.000000] memory[0x10] [0x00000000fe723000-0x00000000fe723fff],
0x0000000000001000 bytes flags: 0x0
[ 0.000000] memory[0x11] [0x00000000fe724000-0x00000000fe724fff],
0x0000000000001000 bytes flags: 0x4
[ 0.000000] memory[0x12] [0x00000000fe725000-0x00000000fe725fff],
0x0000000000001000 bytes flags: 0x0
[ 0.000000] memory[0x13] [0x00000000fe726000-0x00000000fe726fff],
0x0000000000001000 bytes flags: 0x4
[ 0.000000] memory[0x14] [0x00000000fe727000-0x00000000fe728fff],
0x0000000000002000 bytes flags: 0x0
[ 0.000000] memory[0x15] [0x00000000fe729000-0x00000000fe729fff],
0x0000000000001000 bytes flags: 0x4
[ 0.000000] memory[0x16] [0x00000000fe72a000-0x00000000fe72afff],
0x0000000000001000 bytes flags: 0x0
[ 0.000000] memory[0x17] [0x00000000fe72b000-0x00000000fe72cfff],
0x0000000000002000 bytes flags: 0x4
[ 0.000000] memory[0x18] [0x00000000fe72d000-0x00000000fe72dfff],
0x0000000000001000 bytes flags: 0x0
[ 0.000000] memory[0x19] [0x00000000fe72e000-0x00000000fe72efff],
0x0000000000001000 bytes flags: 0x4
[ 0.000000] memory[0x1a] [0x00000000fe72f000-0x00000000fe72ffff],
0x0000000000001000 bytes flags: 0x0
[ 0.000000] memory[0x1b] [0x00000000fe730000-0x00000000fe730fff],
0x0000000000001000 bytes flags: 0x4
[ 0.000000] memory[0x1c] [0x00000000fe731000-0x00000000fe731fff],
0x0000000000001000 bytes flags: 0x0
[ 0.000000] memory[0x1d] [0x00000000fe732000-0x00000000fe732fff],
0x0000000000001000 bytes flags: 0x4
[ 0.000000] memory[0x1e] [0x00000000fe733000-0x00000000fe733fff],
0x0000000000001000 bytes flags: 0x0
[ 0.000000] memory[0x1f] [0x00000000fe734000-0x00000000fe734fff],
0x0000000000001000 bytes flags: 0x4
[ 0.000000] memory[0x20] [0x00000000fe735000-0x00000000fe736fff],
0x0000000000002000 bytes flags: 0x0
[ 0.000000] memory[0x21] [0x00000000fe737000-0x00000000fe737fff],
0x0000000000001000 bytes flags: 0x4
[ 0.000000] memory[0x22] [0x00000000fe738000-0x00000000fff60fff],
0x0000000001829000 bytes flags: 0x0
[ 0.000000] memory[0x23] [0x00000000fff61000-0x00000000fff61fff],
0x0000000000001000 bytes flags: 0x4
[ 0.000000] memory[0x24] [0x00000000fff62000-0x000000047fffffff],
0x000000038009e000 bytes flags: 0x0
[ 0.000000] reserved.cnt = 0xd
[ 0.000000] reserved[0x0] [0x0000000080000000-0x000000008007ffff],
0x0000000000080000 bytes flags: 0x0
[ 0.000000] reserved[0x1] [0x0000000080200000-0x00000000815fffff],
0x0000000001400000 bytes flags: 0x0
[ 0.000000] reserved[0x2] [0x0000000087f00000-0x0000000087f05fff],
0x0000000000006000 bytes flags: 0x0
[ 0.000000] reserved[0x3] [0x00000000db0a2000-0x00000000db0a48b4],
0x00000000000028b5 bytes flags: 0x0
[ 0.000000] reserved[0x4] [0x00000000db2a2000-0x00000000dc709fff],
0x0000000001468000 bytes flags: 0x0
[ 0.000000] reserved[0x5] [0x00000000fe701000-0x00000000fe701fff],
0x0000000000001000 bytes flags: 0x0
[ 0.000000] reserved[0x6] [0x00000000fe704040-0x00000000fe70404f],
0x0000000000000010 bytes flags: 0x0
[ 0.000000] reserved[0x7] [0x000000046ffe1d40-0x000000047dfe253f],
0x000000000e000800 bytes flags: 0x0
[ 0.000000] reserved[0x8] [0x000000047dfe2548-0x000000047dfe2578],
0x0000000000000031 bytes flags: 0x0
[ 0.000000] reserved[0x9] [0x000000047dfe2580-0x000000047dfe25ae],
0x000000000000002f bytes flags: 0x0
[ 0.000000] reserved[0xa] [0x000000047dfe25b0-0x000000047dfe25de],
0x000000000000002f bytes flags: 0x0
[ 0.000000] reserved[0xb] [0x000000047dfe25e0-0x000000047dfefffb],
0x000000000000da1c bytes flags: 0x0
[ 0.000000] reserved[0xc] [0x000000047dff0000-0x000000047fffffff],
0x0000000002010000 bytes flags: 0x0

Best regards

Heinrich

>
> >
> > Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@xxxxxxxxxxxxx>
> > ---
> > arch/riscv/Kconfig | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index 4f7b70ae7c31..a6e57614c3fd 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -31,6 +31,7 @@ config RISCV
> >       select ARCH_HAS_STRICT_KERNEL_RWX if MMU && !XIP_KERNEL
> >       select ARCH_HAS_STRICT_MODULE_RWX if MMU && !XIP_KERNEL
> >       select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
> > +    select ARCH_KEEP_MEMBLOCK
> >       select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
> >       select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
> >       select ARCH_SUPPORTS_HUGETLBFS if MMU

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