Re: [PATCH v5 1/2] mm: Abstract THP allocation

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2024/9/24 20:17, Dev Jain wrote:
> 
> On 9/24/24 16:50, Kefeng Wang wrote:
>>
>>
>> On 2024/9/24 18:16, Dev Jain wrote:
>>> In preparation for the second patch, abstract away the THP allocation
>>> logic present in the create_huge_pmd() path, which corresponds to the
>>> faulting case when no page is present.
>>>
>>> There should be no functional change as a result of applying this patch,
>>> except that, as David notes at [1], a PMD-aligned address should
>>> be passed to update_mmu_cache_pmd().
>>>
>>> [1]: https://lore.kernel.org/all/ddd3fcd2-48b3-4170- 
>>> bcaa-2fe66e093f43@redhat.com/
>>>
>>> Acked-by: David Hildenbrand <david@redhat.com>
>>> Signed-off-by: Dev Jain <dev.jain@arm.com>
>>> ---
>>>   mm/huge_memory.c | 98 ++++++++++++++++++++++++++++--------------------
>>>   1 file changed, 57 insertions(+), 41 deletions(-)
>>>
>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>> index 4e34b7f89daf..bdbf67c18f6c 100644
>>> --- a/mm/huge_memory.c
>>> +++ b/mm/huge_memory.c
>>> @@ -1148,47 +1148,81 @@ unsigned long thp_get_unmapped_area(struct 
>>> file *filp, unsigned long addr,
>>>   }
>>>   EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
>>>   -static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
>>> -            struct page *page, gfp_t gfp)
>>> +static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct 
>>> *vma,
>>> +                          unsigned long addr)
>>>   {
>>> -    struct vm_area_struct *vma = vmf->vma;
>>> -    struct folio *folio = page_folio(page);
>>> -    pgtable_t pgtable;
>>> -    unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
>>> -    vm_fault_t ret = 0;
>>> +    unsigned long haddr = addr & HPAGE_PMD_MASK;
>>> +    gfp_t gfp = vma_thp_gfp_mask(vma);
>>> +    const int order = HPAGE_PMD_ORDER;
>>> +    struct folio *folio = vma_alloc_folio(gfp, order, vma, haddr, 
>>> true);
>>
>> There is a warning without NUMA,
>>
>> ../mm/huge_memory.c: In function ‘vma_alloc_anon_folio_pmd’:
>> ../mm/huge_memory.c:1154:16: warning: unused variable ‘haddr’ [- 
>> Wunused-variable]
>>  1154 |  unsigned long haddr = addr & HPAGE_PMD_MASK;
>>       |                ^~~~~
>>
> 
> But why is this happening?

If no CONFIG_NUMA, vma_alloc_folio(...) = folio_alloc_noprof(gfp, order),
it won't use haddr.