On 10.11.25 11:33, Christophe Leroy wrote:
Le 10/11/2025 à 11:10, David Hildenbrand (Red Hat) a écrit :
[fighting with mail transitioning, for some reason I did not receive
the mails from Christophe, so replying here]
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index e24f4d88885ae..55c3626c86273 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -137,6 +137,7 @@ config PPC
select ARCH_HAS_DMA_OPS if PPC64
select ARCH_HAS_FORTIFY_SOURCE
select ARCH_HAS_GCOV_PROFILE_ALL
+ select ARCH_HAS_GIGANTIC_PAGE if PPC64
The patch looks good from PPC64 perspective, it also fixes the problem
reported on corenet64_smp_defconfig...
Problem is not only on PPC64, it is on PPC32 as well, for instance
corenet32_smp_defconfig has the problem as well.
However on looking deeper into it - I agree with Christophe that this
problem might still exist on PPC32.
Ah, I missed that. I thought it would be a ppc64 thing. :(
I did try the patch on corenet32_smp_defconfig and I can see the WARN_ON
still triggering. You can check the logs here..
https://eur01.safelinks.protection.outlook.com/?
url=https%3A%2F%2Fgithub.com%2Friteshharjani%2Flinux-
ci%2Factions%2Fruns%2F19169468405%2Fjob%2F54799498288&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cf2e19b221ba740b2034e08de204158de%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638983662203106300%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=UKQnlJWDKPfNCiYL8W7d2%2FTAhMhGbmxx8IDvy8jTbNQ%3D&reserved=0
So I think what you want instead is:
diff --git a/arch/powerpc/platforms/Kconfig.cputype
b/arch/powerpc/platforms/Kconfig.cputype
index 7b527d18aa5ee..1f5a1e587740c 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -276,6 +276,7 @@ config PPC_E500
select FSL_EMB_PERFMON
bool
select ARCH_SUPPORTS_HUGETLBFS if PHYS_64BIT || PPC64
+ select ARCH_HAS_GIGANTIC_PAGE if ARCH_SUPPORTS_HUGETLBFS
select PPC_SMP_MUXED_IPI
select PPC_DOORBELL
select PPC_KUEP
@Christophe,
I don't think even the above diff will fix the warning on PPC32.
The patch defines MAX_FOLIO_ORDER as P4D_ORDER...
+#define MAX_FOLIO_ORDER P4D_ORDER
+#define P4D_ORDER (P4D_SHIFT - PAGE_SHIFT)
and for ppc32 in..
include/asm-generic/pgtable-nop4d.h
#define P4D_SHIFT PGDIR_SHIFT
Then in..
arch/powerpc/include/asm/nohash/32/pgtable.h
#define PGDIR_SHIFT (PAGE_SHIFT + PTE_INDEX_SIZE)
#define PTE_INDEX_SIZE PTE_SHIFT
in...
arch/powerpc/include/asm/page_32.h
#define PTE_SHIFT (PAGE_SHIFT - PTE_T_LOG2) /* full page */
#define PTE_T_LOG2 (__builtin_ffs(sizeof(pte_t)) - 1)
So if you see from above P4D_ORDER is coming down to PTE_INDEX_SIZE
IIUC, that will cause MAX_FOLIO_ORDER to be 9 in case of e500mc
machine type right?
Can you please confirm if the above analysis looks correct to you?
Cristophe wrote
"
Ah you are right, that's not enough. I was thinking that PGDIR_ORDER was
the highest possible value ever but in fact not. PGDIR_SIZE is 4Mbytes
so any page larger than that still triggers the warning. Here are the
warnings I get on QEMU with corenet32_smp_defconfig
"
And then we get
HugeTLB: registered 1.00 GiB page size, pre-allocated 0 pages
HugeTLB: 0 KiB vmemmap can be freed for a 1.00 GiB page
HugeTLB: registered 64.0 MiB page size, pre-allocated 1 pages
HugeTLB: 0 KiB vmemmap can be freed for a 64.0 MiB page
HugeTLB: registered 256 MiB page size, pre-allocated 1 pages
HugeTLB: 0 KiB vmemmap can be freed for a 256 MiB page
HugeTLB: registered 4.00 MiB page size, pre-allocated 0 pages
HugeTLB: 0 KiB vmemmap can be freed for a 4.00 MiB page
HugeTLB: registered 16.0 MiB page size, pre-allocated 0 pages
HugeTLB: 0 KiB vmemmap can be freed for a 16.0 MiB page
How could any of these larger sizes possibly ever get mapped into a page
table on 32bit? I'm probably missing something important :)
Using contiguous entries in a table to describe larger pages.
Thanks, that makes sense.
Alright, let me think whether we should just have a generic "unlimited"
thing here (e.g., max_order = 31).
--
Cheers
David
