On 2024/6/11 18:11, Baolin Wang wrote:
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.
Keep the same behavior (per-page fault) for non-anon shmem to avoid inflating
the RSS unintentionally, and we can discuss what size of mapping to build
when extending mTHP to control non-anon shmem in the future.
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
mm/memory.c | 57 +++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 47 insertions(+), 10 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index eef4e482c0c2..72775ee99ff3 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;
+ unsigned long addr = vmf->address;
/* Did we COW the page? */
if (is_cow)
@@ -4864,24 +4867,58 @@ 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;
+
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;
addr -= idx * PAGE_SIZE;
+ page = &folio->page;
+ }
+ }
+
vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
- vmf->address, &vmf->ptl);
+ addr, &vmf->ptl);
no newline now,
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)) {
+ update_mmu_tlb_range(vma, addr, vmf->pte, nr_pages);
ret = VM_FAULT_NOPAGE;
+ goto unlock;
}
We may add a vmf_pte_range_changed(), but separate it.
Some very small nits, up to you,
Reviewed-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
+ 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;
}
