Re: [PATCH v4 1/2] mm: Abstract THP allocation

[David Hildenbrand <david@redhat.com>]

On 24.09.24 06:25, Dev Jain wrote:
> 
> On 9/17/24 17:17, David Hildenbrand wrote:
>> On 16.09.24 11:43, 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/
>>>
>>> Signed-off-by: Dev Jain <dev.jain@arm.com>
>>> ---
>>>    mm/huge_memory.c | 108 +++++++++++++++++++++++++++++------------------
>>>    1 file changed, 66 insertions(+), 42 deletions(-)
>>>
>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>> index 2a73efea02d7..cdc632b8dc9c 100644
>>> --- a/mm/huge_memory.c
>>> +++ b/mm/huge_memory.c
>>> @@ -1146,47 +1146,88 @@ 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);
>>>    -    VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
>>> +    if (unlikely(!folio)) {
>>> +        count_vm_event(THP_FAULT_FALLBACK);
>>> +        count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
>>> +        goto out;
>>> +    }
>>>    +    VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
>>>        if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
>>>            folio_put(folio);
>>>            count_vm_event(THP_FAULT_FALLBACK);
>>>            count_vm_event(THP_FAULT_FALLBACK_CHARGE);
>>> -        count_mthp_stat(HPAGE_PMD_ORDER,
>>> MTHP_STAT_ANON_FAULT_FALLBACK);
>>> -        count_mthp_stat(HPAGE_PMD_ORDER,
>>> MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
>>> -        return VM_FAULT_FALLBACK;
>>> +        count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
>>> +        count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
>>> +        return NULL;
>>>        }
>>>        folio_throttle_swaprate(folio, gfp);
>>>    -    pgtable = pte_alloc_one(vma->vm_mm);
>>> -    if (unlikely(!pgtable)) {
>>> -        ret = VM_FAULT_OOM;
>>> -        goto release;
>>> -    }
>>> -
>>> -    folio_zero_user(folio, vmf->address);
>>> +    folio_zero_user(folio, addr);
>>>        /*
>>>         * The memory barrier inside __folio_mark_uptodate makes sure that
>>>         * folio_zero_user writes become visible before the set_pmd_at()
>>>         * write.
>>>         */
>>>        __folio_mark_uptodate(folio);
>>> +out:
>>> +    return folio;
>>> +}
>>> +
>>> +static void __pmd_thp_fault_success_stats(struct vm_area_struct *vma)
>>> +{
>>> +    count_vm_event(THP_FAULT_ALLOC);
>>> +    count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_ALLOC);
>>> +    count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC);
>>> +}
>>
>> just inline that into map_anon_folio_pmd(), please. map_anon_folio_pmd
>> is perfectly readable ;)
> 
> If you are asking me to open code it in map_anon_folio_pmd(), I'll do that.

Yes, there will be a single user, so just keep it in the caller.

-- 
Cheers,

David / dhildenb