On 9/11/24 16:22, Kefeng Wang wrote:

On 2024/9/11 14:55, Dev Jain wrote:

quoted

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@arm.com>
---
  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;

Maybe move vma_thp_gfp_mask() into this function too.

That's better, thanks.

quoted

+    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;

We need to return NULL here as folio not set to null,

My bad for assuming that folio_put() also sets folio to NULL. I read
through the code path for that and I guess it does not. Thanks.

quoted

      }
      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;
+}
+