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

[Dev Jain <dev.jain@arm.com>]

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?

>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index c584e77efe10..147a6e069c71 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1151,11 +1151,11 @@ EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
>  static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct 
> *vma,
>                                               unsigned long addr)
>  {
> -       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);
> +       struct folio *folio;
>
> +       folio = vma_alloc_folio(gfp, order, vma, addr & 
> HPAGE_PMD_MASK, true);
>         if (unlikely(!folio)) {
>                 count_vm_event(THP_FAULT_FALLBACK);
>                 count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
>
>>   - 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;
>
> Maybe return NULL to omit the out?

Ah sorry, I have made a mess of unnecessary delayed returns :)
>
>
> Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>

Thanks!
>
>
>> +    }
>>   +    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 map_anon_folio_pmd(struct folio *folio, pmd_t *pmd,
>> +                   struct vm_area_struct *vma, unsigned long haddr)
>> +{
>> +    pmd_t entry;
>> +
>> +    entry = mk_huge_pmd(&folio->page, vma->vm_page_prot);
>> +    entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
>> +    folio_add_new_anon_rmap(folio, vma, haddr, RMAP_EXCLUSIVE);
>> +    folio_add_lru_vma(folio, vma);
>> +    set_pmd_at(vma->vm_mm, haddr, pmd, entry);
>> +    update_mmu_cache_pmd(vma, haddr, pmd);
>> +    add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
>> +    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);
>> +}
>> +
>> +static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf)
>> +{
>> +    unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
>> +    struct vm_area_struct *vma = vmf->vma;
>> +    struct folio *folio;
>> +    pgtable_t pgtable;
>> +    vm_fault_t ret = 0;
>> +
>> +    folio = vma_alloc_anon_folio_pmd(vma, vmf->address);
>> +    if (unlikely(!folio))
>> +        return VM_FAULT_FALLBACK;
>> +
>> +    pgtable = pte_alloc_one(vma->vm_mm);
>> +    if (unlikely(!pgtable)) {
>> +        ret = VM_FAULT_OOM;
>> +        goto release;
>> +    }
>>         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
>>       if (unlikely(!pmd_none(*vmf->pmd))) {
>>           goto unlock_release;
>>       } else {
>> -        pmd_t entry;
>> -
>>           ret = check_stable_address_space(vma->vm_mm);
>>           if (ret)
>>               goto unlock_release;
>> @@ -1202,21 +1236,11 @@ static vm_fault_t 
>> __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
>>               VM_BUG_ON(ret & VM_FAULT_FALLBACK);
>>               return ret;
>>           }
>> -
>> -        entry = mk_huge_pmd(page, vma->vm_page_prot);
>> -        entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
>> -        folio_add_new_anon_rmap(folio, vma, haddr, RMAP_EXCLUSIVE);
>> -        folio_add_lru_vma(folio, vma);
>>           pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
>> -        set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
>> -        update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
>> -        add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
>> +        map_anon_folio_pmd(folio, vmf->pmd, vma, haddr);
>>           mm_inc_nr_ptes(vma->vm_mm);
>>           deferred_split_folio(folio, false);
>>           spin_unlock(vmf->ptl);
>> -        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);
>>       }
>>         return 0;
>> @@ -1283,8 +1307,6 @@ static void set_huge_zero_folio(pgtable_t 
>> pgtable, struct mm_struct *mm,
>>   vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
>>   {
>>       struct vm_area_struct *vma = vmf->vma;
>> -    gfp_t gfp;
>> -    struct folio *folio;
>>       unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
>>       vm_fault_t ret;
>>   @@ -1335,14 +1357,8 @@ vm_fault_t do_huge_pmd_anonymous_page(struct 
>> vm_fault *vmf)
>>           }
>>           return ret;
>>       }
>> -    gfp = vma_thp_gfp_mask(vma);
>> -    folio = vma_alloc_folio(gfp, HPAGE_PMD_ORDER, vma, haddr, true);
>> -    if (unlikely(!folio)) {
>> -        count_vm_event(THP_FAULT_FALLBACK);
>> -        count_mthp_stat(HPAGE_PMD_ORDER, 
>> MTHP_STAT_ANON_FAULT_FALLBACK);
>> -        return VM_FAULT_FALLBACK;
>> -    }
>> -    return __do_huge_pmd_anonymous_page(vmf, &folio->page, gfp);
>> +
>> +    return __do_huge_pmd_anonymous_page(vmf);
>>   }
>>     static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned 
>> long addr,
>