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

[David Hildenbrand <david@redhat.com>]

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 ;)

> +
> +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);
> +	__pmd_thp_fault_success_stats(vma);
> +}
> +
> +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;
> +	pgtable_t pgtable = NULL;
> +	struct folio *folio;
> +	vm_fault_t ret = 0;
> +
> +	folio = vma_alloc_anon_folio_pmd(vma, vmf->address);
> +	if (unlikely(!folio)) {
> +		ret = VM_FAULT_FALLBACK;
> +		goto release;

Why not simply "return VM_FAULT_FALLBACK;" ? There is nothing to 
release. Then you can avoid the

"if (folio)" below and even stop initializing pgtable to NULL.


With these things take care of

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb