On 7/11/23 9:14 PM, David Hildenbrand wrote:
> On 11.07.23 17:40, Aneesh Kumar K V wrote:
>> 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?
>
> IMHO not an issue. The common code check is a bit weaker and the arch check a
> bit stronger.
>
>>
ok will update
>> 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
>
> s/contianed/contained/
>
>> + * so that we always allocate vmemmap memory from altmap area.
>
> In theory, it's not only the vmemmap size, but also the vmemmap start (that
> it doesn't start somewhere in between a page, crossing a page). I suspect the
> start is always guaranteed to be aligned (of the vmemmap size is aligned),
> correct?
>
That is correct.
>> + */
>> + if (!IS_ALIGNED(vmemmap_size, PAGE_SIZE))
>> + return false;
>> /*
>> * Without page reservation remaining pages should be pageblock
>> aligned.
>> */
>>
-aneesh
>
