On 7/11/23 8:56 PM, David Hildenbrand wrote:
> On 11.07.23 06:48, 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. Hence we skip the
>> restrictions w.r.t vmemmap size to be multiple of PMD_SIZE. This also
>> makes the feature widely useful because to use PMD_SIZE vmemmap area we
>> require a memory block size of 2GiB
>>
>> We can also use MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY to that the feature
>> can work with a memory block size of 256MB. Using altmap.reserve feature
>> to align things correctly at pageblock granularity. We can end up
>> losing some pages in memory with this. For ex: with a 256MiB 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.ku...@linux.ibm.com>
>> ---
>> arch/powerpc/Kconfig | 1 +
>> arch/powerpc/include/asm/pgtable.h | 28 +++++++++++++++++++
>> .../platforms/pseries/hotplug-memory.c | 3 +-
>> mm/memory_hotplug.c | 2 ++
>> 4 files changed, 33 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/include/asm/pgtable.h
>> b/arch/powerpc/include/asm/pgtable.h
>> index 68817ea7f994..8e6c92dde6ad 100644
>> --- a/arch/powerpc/include/asm/pgtable.h
>> +++ b/arch/powerpc/include/asm/pgtable.h
>> @@ -169,6 +169,34 @@ static inline bool is_ioremap_addr(const void *x)
>> int __meminit vmemmap_populated(unsigned long vmemmap_addr, int
>> vmemmap_map_size);
>> bool altmap_cross_boundary(struct vmem_altmap *altmap, unsigned long start,
>> unsigned long page_size);
>> +/*
>> + * 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
>> + * alignment requirement is met using altmap->reserve blocks.
>> + */
>> +#define arch_supports_memmap_on_memory arch_supports_memmap_on_memory
>> +static inline bool arch_supports_memmap_on_memory(unsigned long size)
>> +{
>> + unsigned long nr_pages = size >> PAGE_SHIFT;
>> + unsigned long vmemmap_size = nr_pages * sizeof(struct page);
>> +
>> + if (!radix_enabled())
>> + return false;
>> +
>> +#ifdef CONFIG_PPC_4K_PAGES
>> + return IS_ALIGNED(vmemmap_size, PMD_SIZE);
>> +#else
>> + /*
>> + * Make sure the vmemmap allocation is fully contianed
>> + * so that we always allocate vmemmap memory from altmap area.
>> + * The pageblock alignment requirement is met by using
>> + * reserve blocks in altmap.
>> + */
>> + return IS_ALIGNED(vmemmap_size, PAGE_SIZE);
>
> Can we move that check into common code as well?
>
> If our (original) vmemmap size would not fit into a single page, we would be
> in trouble on any architecture. Did not check if it would be an issue for
> arm64 as well in case we would allow eventually wasting memory.
>
For x86 and arm we already do IS_ALIGNED(vmemmap_size, PMD_SIZE); in
arch_supports_memmap_on_memory(). That should imply PAGE_SIZE alignment.
If arm64 allow the usage of altmap.reserve, I would expect the
arch_supports_memmap_on_memory to have the PAGE_SIZE check.
Adding the PAGE_SIZE check in mhp_supports_memmap_on_memory() makes it
redundant check for x86 and arm currently?
modified mm/memory_hotplug.c
@@ -1293,6 +1293,13 @@ static bool mhp_supports_memmap_on_memory(unsigned long
size)
*/
if (!mhp_memmap_on_memory() || size != memory_block_size_bytes())
return false;
+
+ /*
+ * Make sure the vmemmap allocation is fully contianed
+ * so that we always allocate vmemmap memory from altmap area.
+ */
+ if (!IS_ALIGNED(vmemmap_size, PAGE_SIZE))
+ return false;
/*
* Without page reservation remaining pages should be pageblock
aligned.
*/
