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

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Message-ID: <59b38cc6-9491-40bf-a254-9c6c5f07c072@arm.com>
Date: Wed, 25 Sep 2024 10:58:43 +0530
From: Dev Jain <dev.jain@....com>
To: Kefeng Wang <wangkefeng.wang@...wei.com>, akpm@...ux-foundation.org,
 david@...hat.com, willy@...radead.org, kirill.shutemov@...ux.intel.com
Cc: ryan.roberts@....com, anshuman.khandual@....com, catalin.marinas@....com,
 cl@...two.org, vbabka@...e.cz, mhocko@...e.com, apopple@...dia.com,
 dave.hansen@...ux.intel.com, will@...nel.org, baohua@...nel.org,
 jack@...e.cz, mark.rutland@....com, hughd@...gle.com,
 aneesh.kumar@...nel.org, yang@...amperecomputing.com, peterx@...hat.com,
 ioworker0@...il.com, jglisse@...gle.com, ziy@...dia.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org
Subject: Re: [PATCH v5 1/2] mm: Abstract THP allocation


On 9/24/24 18:24, Kefeng Wang wrote:
>
>
> 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@...hat.com/
>>>>
>>>> Acked-by: David Hildenbrand <david@...hat.com>
>>>> Signed-off-by: Dev Jain <dev.jain@....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.

Ah got it, thanks, I missed the ifdeffery in include/linux/gfp.h.
>
>