[PATCH v3 1/2] mm: Abstract THP allocation

[Dev Jain]

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.

Signed-off-by: Dev Jain <dev.jain@xxxxxxx>
---
 mm/huge_memory.c | 110 +++++++++++++++++++++++++++++------------------
 1 file changed, 67 insertions(+), 43 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 67c86a5d64a6..b96a1ff2bf40 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -943,47 +943,88 @@ 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 *pmd_thp_fault_alloc(gfp_t gfp, struct vm_area_struct *vma,
+					 unsigned long haddr, 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;
+	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);
+		goto out;
 	}
 	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);
+}
+
+static void map_pmd_thp(struct folio *folio, struct vm_fault *vmf,
+			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, vmf->pmd, entry);
+	update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
+	add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
+	mm_inc_nr_ptes(vma->vm_mm);
+}
+
+static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct folio *folio;
+	pgtable_t pgtable;
+	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
+	vm_fault_t ret = 0;
+	gfp_t gfp = vma_thp_gfp_mask(vma);
+
+	folio = pmd_thp_fault_alloc(gfp, vma, haddr, vmf->address);
+	if (unlikely(!folio)) {
+		ret = VM_FAULT_FALLBACK;
+		goto release;
+	}
+
+	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;
@@ -997,20 +1038,10 @@ 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);
-		mm_inc_nr_ptes(vma->vm_mm);
+		map_pmd_thp(folio, vmf, vma, haddr);
 		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);
+		__pmd_thp_fault_success_stats(vma);
 	}
 
 	return 0;
@@ -1019,7 +1050,8 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
 release:
 	if (pgtable)
 		pte_free(vma->vm_mm, pgtable);
-	folio_put(folio);
+	if (folio)
+		folio_put(folio);
 	return ret;
 
 }
@@ -1077,8 +1109,6 @@ 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;
 
@@ -1129,14 +1159,8 @@ 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,
-- 
2.30.2