From: Michael Ellerman <mpe@ellerman.id.au>
To: victora <victora@linux.vnet.ibm.com>,
alistair@popple.id.au, jk@ozlabs.org
Cc: victora@br.ibm.com, mauricfo@linux.vnet.ibm.com, linuxppc-dev@ozlabs.org
Subject: Re: 1M hugepage size being registered on Linux
Date: Thu, 22 Jun 2017 13:59:40 +1000 [thread overview]
Message-ID: <87o9tgsmdv.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <322aa4a1a11ca79008a8c894c12a80d5@linux.vnet.ibm.com>
Hi Victor,
Someone refreshed my memory on this, coffee was involved ...
victora <victora@linux.vnet.ibm.com> writes:
> Hi Alistair/Jeremy,
>
> I am working on a bug related to 1M hugepage size being registered on
> Linux (Power 8 Baremetal - Garrison).
On those machines the property in the device tree comes straight from
hostboot, and it includes 1M:
# lsprop ibm,segment-page-sizes
ibm,segment-page-sizes
0000000c 00000000 00000003 0000000c
baseshift slbenc lpnum shift
00000000 00000010 00000007 00000018
penc shift penc shift
00000038 00000010 00000110 00000002
penc baseshift slbenc lpnum
00000010 00000001 00000018 00000008
shift penc shift penc
00000014 00000130 00000001 00000014 <--- 1MB = 2^0x14
baseshift slbenc lpnum shift
00000002 00000018 00000100 00000001
penc baseshift slbenc lpnum
00000018 00000000 00000022 00000120
shift penc baseshift slbenc
00000001 00000022 00000003
lpnum shift penc
> I was checking dmesg and it seems that 1M page size is coming from
> firmware to Linux.
>
> [ 0.000000] base_shift=20: shift=20, sllp=0x0130, avpnm=0x00000000, tlbiel=0, penc=2
> [ 1.528867] HugeTLB registered 1 MB page size, pre-allocated 0 pages
Which is why you see that message.
> Should Linux support this page size? As afar as I know, this was an
> unsupported page size in the past isn't it? If this should be supported
> now, is there any specific reason for that?
It's unsupported in Linux because it doesn't match the page table
geometry.
We merged a patch from Aneesh to filter it out in 4.12-rc1:
a525108cf1cc ("powerpc/mm/hugetlb: Filter out hugepage size not supported by page table layout")
I guess we should probably send that patch to stable et. al.
cheers
next prev parent reply other threads:[~2017-06-22 3:59 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-20 13:47 1M hugepage size being registered on Linux victora
2017-06-21 10:33 ` Michael Ellerman
2017-06-21 15:32 ` Mauricio Faria de Oliveira
2017-06-22 8:54 ` Balbir Singh
2017-06-22 8:21 ` Benjamin Herrenschmidt
2017-06-22 3:59 ` Michael Ellerman [this message]
2017-06-22 8:09 ` Benjamin Herrenschmidt
2017-06-22 11:17 ` Michael Ellerman
2017-06-23 19:00 ` victora
2017-06-26 3:14 ` Michael Ellerman
2017-06-22 11:03 ` Michal Suchánek
2017-06-23 5:26 ` Michael Ellerman
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