On 06.07.23 10:50, Aneesh Kumar K.V wrote:
Radix vmemmap mapping can map things correctly at the PMD level or PTE
level based on different device boundary checks. We also use altmap.reserve
feature to align things correctly at pageblock granularity. We can end up
loosing some pages in memory with this. For ex: with 256MB memory block
size, we require 4 pages to map vmemmap pages, In order to align things
correctly we end up adding a reserve of 28 pages. ie, for every 4096 pages
28 pages get reserved.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/mm/book3s64/radix_pgtable.c | 28 +++++++++++++++++++
.../platforms/pseries/hotplug-memory.c | 4 ++-
3 files changed, 32 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 116d6add0bb0..f890907e5bbf 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -157,6 +157,7 @@ config PPC
select ARCH_HAS_UBSAN_SANITIZE_ALL
select ARCH_HAVE_NMI_SAFE_CMPXCHG
select ARCH_KEEP_MEMBLOCK
+ select ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE if PPC_RADIX_MMU
select ARCH_MIGHT_HAVE_PC_PARPORT
select ARCH_MIGHT_HAVE_PC_SERIO
select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c
index a62729f70f2a..c0bd60b5fb64 100644
--- a/arch/powerpc/mm/book3s64/radix_pgtable.c
+++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
@@ -1678,3 +1678,31 @@ int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)
return 1;
}
+
+/*
+ * mm/memory_hotplug.c:mhp_supports_memmap_on_memory goes into details
+ * some of the restrictions. We don't check for PMD_SIZE because our
+ * vmemmap allocation code can fallback correctly. The pageblock
x86 also has the fallback IIRC; the concern is rather that you end up
with a PTE-mapped vmemmap, which is slower at runtime than a PMD-mapped
vmemmap.
+ * alignment requirement is met using altmap->reserve blocks.
+ */
+bool mhp_supports_memmap_on_memory(unsigned long size)
+{
+ if (!radix_enabled())
+ return false;
+ /*
+ * The pageblock alignment requirement is met by using
+ * reserve blocks in altmap.
+ */
+ return size == memory_block_size_bytes();
+}
I really dislike such arch overrides.
I think the flow should be something like that, having a generic:
bool mhp_supports_memmap_on_memory(unsigned long size)
{
...
return arch_mhp_supports_memmap_on_memory(size)) &&
size == memory_block_size_bytes() &&
...
}
where we'll also keep the pageblock check here.
And a ppc specific
bool arch_mhp_supports_memmap_on_memory(unsigned long size)
{
/*
* Don't check for the vmemmap covering PMD_SIZE, we accept that
* we might get a PTE-mapped vmemmap.
*/
return radix_enabled();
}
We can then move the PMD_SIZE check into arch specific code (x86-aarch64).
--
Cheers,
David / dhildenb
