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

Baolin Wang
2024-06-03T08:04:43Z

On 2024/6/3 12:44, Lance Yang wrote:
> On Thu, May 30, 2024 at 10:04 AM Baolin Wang
> <baolin.wang@linux.alibaba.com> 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.
>>
>> 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);
>
> Just a friendly reminder: Bang has added the update_mmu_tlb_range()[1] batch
> function to update TLB in batches, so we can use it instead of the
> update_mmu_tlb()
> loop.
>
> [1] https://lore.kernel.org/linux-mm/20240522061204.117421-1-libang.li@antgroup.com/

Good point, I will use the new helper instead.