Barry Song <21cnbao@xxxxxxxxx> writes: > On Tue, Apr 16, 2024 at 2:41 PM Huang, Ying <ying.huang@xxxxxxxxx> wrote: >> >> Barry Song <21cnbao@xxxxxxxxx> writes: >> >> > On Tue, Apr 16, 2024 at 2:27 PM Huang, Ying <ying.huang@xxxxxxxxx> wrote: >> >> >> >> >> >> Added Khalid for arch_do_swap_page(). >> >> >> >> Barry Song <21cnbao@xxxxxxxxx> writes: >> >> >> >> > On Mon, Apr 15, 2024 at 8:39 PM Huang, Ying <ying.huang@xxxxxxxxx> wrote: >> >> >> >> >> >> Barry Song <21cnbao@xxxxxxxxx> writes: >> >> >> >> [snip] >> >> >> >> >> >> >> >> > + bool any_swap_shared = false; >> >> >> > >> >> >> > if (!pte_unmap_same(vmf)) >> >> >> > goto out; >> >> >> > @@ -4137,6 +4141,35 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >> >> >> > */ >> >> >> > vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address, >> >> >> > &vmf->ptl); >> >> >> >> >> >> We should move pte check here. That is, >> >> >> >> >> >> if (unlikely(!vmf->pte || !pte_same(ptep_get(vmf->pte), vmf->orig_pte))) >> >> >> goto out_nomap; >> >> >> >> >> >> This will simplify the situation for large folio. >> >> > >> >> > the plan is moving the whole code block >> >> > >> >> > if (start_pte && folio_test_large(folio) && folio_test_swapcache(folio)) >> >> > >> >> > after >> >> > if (unlikely(!folio_test_uptodate(folio))) { >> >> > ret = VM_FAULT_SIGBUS; >> >> > goto out_nomap; >> >> > } >> >> > >> >> > though we couldn't be !folio_test_uptodate(folio)) for hitting >> >> > swapcache but it seems >> >> > logically better for future use. >> >> >> >> LGTM, Thanks! >> >> >> >> >> >> >> >> > + >> >> >> > + /* We hit large folios in swapcache */ >> >> >> >> >> >> The comments seems unnecessary because the code tells that already. >> >> >> >> >> >> > + if (start_pte && folio_test_large(folio) && folio_test_swapcache(folio)) { >> >> >> > + int nr = folio_nr_pages(folio); >> >> >> > + int idx = folio_page_idx(folio, page); >> >> >> > + unsigned long folio_start = vmf->address - idx * PAGE_SIZE; >> >> >> > + unsigned long folio_end = folio_start + nr * PAGE_SIZE; >> >> >> > + pte_t *folio_ptep; >> >> >> > + pte_t folio_pte; >> >> >> > + >> >> >> > + if (unlikely(folio_start < max(vmf->address & PMD_MASK, vma->vm_start))) >> >> >> > + goto check_pte; >> >> >> > + if (unlikely(folio_end > pmd_addr_end(vmf->address, vma->vm_end))) >> >> >> > + goto check_pte; >> >> >> > + >> >> >> > + folio_ptep = vmf->pte - idx; >> >> >> > + folio_pte = ptep_get(folio_ptep); >> >> >> >> >> >> It's better to construct pte based on fault PTE via generalizing >> >> >> pte_next_swp_offset() (may be pte_move_swp_offset()). Then we can find >> >> >> inconsistent PTEs quicker. >> >> > >> >> > it seems your point is getting the pte of page0 by pte_next_swp_offset() >> >> > unfortunately pte_next_swp_offset can't go back. on the other hand, >> >> > we have to check the real pte value of the 0nd entry right now because >> >> > swap_pte_batch() only really reads pte from the 1st entry. it assumes >> >> > pte argument is the real value for the 0nd pte entry. >> >> > >> >> > static inline int swap_pte_batch(pte_t *start_ptep, int max_nr, pte_t pte) >> >> > { >> >> > pte_t expected_pte = pte_next_swp_offset(pte); >> >> > const pte_t *end_ptep = start_ptep + max_nr; >> >> > pte_t *ptep = start_ptep + 1; >> >> > >> >> > VM_WARN_ON(max_nr < 1); >> >> > VM_WARN_ON(!is_swap_pte(pte)); >> >> > VM_WARN_ON(non_swap_entry(pte_to_swp_entry(pte))); >> >> > >> >> > while (ptep < end_ptep) { >> >> > pte = ptep_get(ptep); >> >> > >> >> > if (!pte_same(pte, expected_pte)) >> >> > break; >> >> > >> >> > expected_pte = pte_next_swp_offset(expected_pte); >> >> > ptep++; >> >> > } >> >> > >> >> > return ptep - start_ptep; >> >> > } >> >> >> >> Yes. You are right. >> >> >> >> But we may check whether the pte of page0 is same as "vmf->orig_pte - >> >> folio_page_idx()" (fake code). >> > >> > right, that is why we are reading and checking PTE0 before calling >> > swap_pte_batch() >> > right now. >> > >> > folio_ptep = vmf->pte - idx; >> > folio_pte = ptep_get(folio_ptep); >> > if (!is_swap_pte(folio_pte) || non_swap_entry(pte_to_swp_entry(folio_pte)) || >> > swap_pte_batch(folio_ptep, nr, folio_pte, &any_swap_shared) != nr) >> > goto check_pte; >> > >> > So, if I understand correctly, you're proposing that we should directly check >> > PTE0 in swap_pte_batch(). Personally, I don't have any objections to this idea. >> > However, I'd also like to hear the feedback from Ryan and David :-) >> >> I mean that we can replace >> >> !is_swap_pte(folio_pte) || non_swap_entry(pte_to_swp_entry(folio_pte)) >> >> in above code with pte_same() with constructed expected first pte. > > Got it. It could be quite tricky, especially with considerations like > pte_swp_soft_dirty, pte_swp_exclusive, and pte_swp_uffd_wp. We might > require a helper function similar to pte_next_swp_offset() but capable of > moving both forward and backward. For instance: > > pte_move_swp_offset(pte_t pte, long delta) > > pte_next_swp_offset can insteadly call it by: > pte_move_swp_offset(pte, 1); > > Is it what you are proposing? Yes. Exactly. -- Best Regards, Huang, Ying >> >> >> >> >> You need to check the pte of page 0 anyway. >> >> >> >> >> >> >> >> > + if (!is_swap_pte(folio_pte) || non_swap_entry(pte_to_swp_entry(folio_pte)) || >> >> >> > + swap_pte_batch(folio_ptep, nr, folio_pte, &any_swap_shared) != nr) >> >> >> > + goto check_pte; >> >> >> > + >> >> >> > + start_address = folio_start; >> >> >> > + start_pte = folio_ptep; >> >> >> > + nr_pages = nr; >> >> >> > + entry = folio->swap; >> >> >> > + page = &folio->page; >> >> >> > + } >> >> >> > + >> >> >> > +check_pte: >> >> >> > if (unlikely(!vmf->pte || !pte_same(ptep_get(vmf->pte), vmf->orig_pte))) >> >> >> > goto out_nomap; >> >> >> > >> >> >> > @@ -4190,6 +4223,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >> >> >> > */ >> >> >> > exclusive = false; >> >> >> > } >> >> >> > + >> >> >> > + /* Reuse the whole large folio iff all entries are exclusive */ >> >> >> > + if (nr_pages > 1 && any_swap_shared) >> >> >> > + exclusive = false; >> >> >> > } >> >> >> > >> >> [snip] >> >> -- >> Best Regards, >> Huang, Ying