[Linuxppc-users] memmap kernel option on ubuntu 16.04 power8

[Calvin Sze]

"Linuxppc-users" <linuxppc-users-bounces
+calvins=us.ibm.com at lists.ozlabs.org> wrote on 09/27/2017 05:45:56 AM:

> From: Michael Ellerman <mpe at ellerman.id.au>
> To: Brian Horton <brianh at linux.vnet.ibm.com>,
linuxppc-users at lists.ozlabs.org
> Date: 09/27/2017 05:46 AM
> Subject: Re: [Linuxppc-users] memmap kernel option on ubuntu 16.04 power8
> Sent by: "Linuxppc-users" <linuxppc-users-bounces
> +calvins=us.ibm.com at lists.ozlabs.org>
>
> Hi Brian,
>
> Brian Horton <brianh at linux.vnet.ibm.com> writes:
> > Greetings all.
> >
> > I'm trying to run some tests with less memory than what's installed.
the
> > 'mem=128G' option works, but it ends up putting all of the memory on
the
> > first numa node:
>
> It doesn't put memory anywhere, it just clamps the total memory, and it
> happens that the first (lowest address) 128G of RAM is all on node 0.
>
> >     available: 2 nodes (0,8)
> >     node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21
> >     22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
> >       41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62
> >     63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79
> >     node 0 size: 130695 MB
> >     node 0 free: 10765 MB
> >     node 8 cpus: 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97
> >     98 99 100 101 102 103 104 105 106 107 108 109 110 111 112
> >     113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129
> >     130 131 132 133 134 135 136 137 138 139 140 141 142 143 1
> >     44 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159
> >     node 8 size: 0 MB
> >     node 8 free: 0 MB
> >
> >
> > I want 64G on each of the 2 numa nodes. Found this kernel option:
> >
> >          memmap=nn[KMG]$ss[KMG]
> >                          [KNL,ACPI] Mark specific memory as reserved.
> >                          Region of memory to be reserved is from
> ss to ss+nn.
> >                          Example: Exclude memory from
0x18690000-0x1869ffff
> >                                   memmap=64K$0x18690000
> >                                   or
> >                                   memmap=0x10000$0x18690000
> >
> > and it works on x86:
> >
> >     available: 2 nodes (0-1)
> >     node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 24 25 26 27 28 29 30 31 32
33
> >     34 35
> >     node 0 size: 64315 MB
> >     node 0 free: 364 MB
> >     node 1 cpus: 12 13 14 15 16 17 18 19 20 21 22 23 36 37 38 39 40 41
> >     42 43 44 45 46 47
> >     node 1 size: 64507 MB
> >     node 1 free: 134 MB
> >
> >
> > but i can't get it to work on Ubuntu 16.04 Power8.
>
> It's not supported on Power.
>
> Further up in the docs it says:
>
>    memmap=exactmap   [KNL,X86] Enable setting of an exact
>          E820 memory map, as specified by the user.

Hi Michael,


memmap=nn[KMG]@ss[KMG]
                        [KNL] Force usage of a specific region of memory.
                        Region of memory to be used is from ss to ss+nn.


It has only [KNL],  Does it mean the nn[KMG]@ss[KMG] is supported on Power?

Thanks

>
> Where the X86 means x86 only.
>
> > someone said that it worked on RHEL, so maybe it's an Ubuntu-specific
bug..
>
> OK that would be interesting, but I suspect it's not true :)
>
> > thoughts? ideas?
>
> AFAIK there's no way to achieve what you're after, without changing
> kernel code or creating a custom device tree.
>
> The mem= option is very primitive, it just clamps the total as I said
> above, it's not NUMA aware.
>
> What hardware/platform are you trying to do this on? Are you familiar
> with kexec?
>
> cheers
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