[PATCH v3 1/6] mm: memory: extend finish_fault() to support large folio

Baolin Wang
2024-05-30T02:04:40Z

Add large folio mapping establishment support for finish_fault() as a preparation,
to support multi-size THP allocation of anonymous shmem pages in the following
patches.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
mm/memory.c | 58 ++++++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 48 insertions(+), 10 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index eef4e482c0c2..435187ff7ea4 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4831,9 +4831,12 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
{
struct vm_area_struct *vma = vmf->vma;
struct page *page;
+ struct folio *folio;
vm_fault_t ret;
bool is_cow = (vmf->flags & FAULT_FLAG_WRITE) &&
!(vma->vm_flags & VM_SHARED);
+ int type, nr_pages, i;
+ unsigned long addr = vmf->address;

/* Did we COW the page? */
if (is_cow)
@@ -4864,24 +4867,59 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
return VM_FAULT_OOM;
}

+ folio = page_folio(page);
+ nr_pages = folio_nr_pages(folio);
+
+ /*
+ * Using per-page fault to maintain the uffd semantics, and same
+ * approach also applies to non-anonymous-shmem faults to avoid
+ * inflating the RSS of the process.
+ */
+ if (!vma_is_anon_shmem(vma) || unlikely(userfaultfd_armed(vma))) {
+ nr_pages = 1;
+ } else if (nr_pages > 1) {
+ pgoff_t idx = folio_page_idx(folio, page);
+ /* The page offset of vmf->address within the VMA. */
+ pgoff_t vma_off = vmf->pgoff - vmf->vma->vm_pgoff;
+
+ /*
+ * Fallback to per-page fault in case the folio size in page
+ * cache beyond the VMA limits.
+ */
+ if (unlikely(vma_off < idx ||
+ vma_off + (nr_pages - idx) > vma_pages(vma))) {
+ nr_pages = 1;
+ } else {
+ /* Now we can set mappings for the whole large folio. */
+ addr = vmf->address - idx * PAGE_SIZE;
+ page = &folio->page;
+ }
+ }
+
vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
- vmf->address, &vmf->ptl);
+ addr, &vmf->ptl);
if (!vmf->pte)
return VM_FAULT_NOPAGE;

/* Re-check under ptl */
- if (likely(!vmf_pte_changed(vmf))) {
- struct folio *folio = page_folio(page);
- int type = is_cow ? MM_ANONPAGES : mm_counter_file(folio);
-
- set_pte_range(vmf, folio, page, 1, vmf->address);
- add_mm_counter(vma->vm_mm, type, 1);
- ret = 0;
- } else {
- update_mmu_tlb(vma, vmf->address, vmf->pte);
+ if (nr_pages == 1 && unlikely(vmf_pte_changed(vmf))) {
+ update_mmu_tlb(vma, addr, vmf->pte);
ret = VM_FAULT_NOPAGE;
+ goto unlock;
+ } else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) {
+ for (i = 0; i < nr_pages; i++)
+ update_mmu_tlb(vma, addr + PAGE_SIZE * i, vmf->pte + i);
+ ret = VM_FAULT_NOPAGE;
+ goto unlock;
}

+ folio_ref_add(folio, nr_pages - 1);
+ set_pte_range(vmf, folio, page, nr_pages, addr);
+ type = is_cow ? MM_ANONPAGES : mm_counter_file(folio);
+ add_mm_counter(vma->vm_mm, type, nr_pages);
+ ret = 0;
+
+unlock:
pte_unmap_unlock(vmf->pte, vmf->ptl);
return ret;
}
--
2.39.3