| Message ID | 20240122194200.381241-12-david@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/memory: optimize fork() with PTE-mapped THP | expand |
On 22/01/2024 19:42, David Hildenbrand wrote: > ... and conditionally return to the caller if any pte except the first one > is writable. fork() has to make sure to properly write-protect in case any > PTE is writable. Other users (e.g., page unmaping) won't care. > > Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> > --- > mm/memory.c | 26 +++++++++++++++++++++----- > 1 file changed, 21 insertions(+), 5 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 341b2be845b6e..a26fd0669016b 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -955,7 +955,7 @@ static __always_inline void __copy_present_ptes(struct vm_area_struct *dst_vma, > > static inline pte_t __pte_batch_clear_ignored(pte_t pte) > { > - return pte_clear_soft_dirty(pte_mkclean(pte_mkold(pte))); > + return pte_wrprotect(pte_clear_soft_dirty(pte_mkclean(pte_mkold(pte)))); > } > > /* > @@ -963,20 +963,29 @@ static inline pte_t __pte_batch_clear_ignored(pte_t pte) > * pages of the same folio. > * > * All PTEs inside a PTE batch have the same PTE bits set, excluding the PFN. > - * the accessed bit, dirty bit and soft-dirty bit. > + * the accessed bit, dirty bit, soft-dirty bit and writable bit. > + . If "any_writable" is set, it will indicate if any other PTE besides the > + * first (given) PTE is writable. > */ > static inline int folio_pte_batch(struct folio *folio, unsigned long addr, > - pte_t *start_ptep, pte_t pte, int max_nr) > + pte_t *start_ptep, pte_t pte, int max_nr, bool *any_writable) > { > unsigned long folio_end_pfn = folio_pfn(folio) + folio_nr_pages(folio); > const pte_t *end_ptep = start_ptep + max_nr; > pte_t expected_pte = __pte_batch_clear_ignored(pte_next_pfn(pte)); > pte_t *ptep = start_ptep + 1; > + bool writable; > + > + if (any_writable) > + *any_writable = false; > > VM_WARN_ON_FOLIO(!pte_present(pte), folio); > > while (ptep != end_ptep) { > - pte = __pte_batch_clear_ignored(ptep_get(ptep)); > + pte = ptep_get(ptep); > + if (any_writable) > + writable = !!pte_write(pte); > + pte = __pte_batch_clear_ignored(pte); > > if (!pte_same(pte, expected_pte)) > break; > @@ -989,6 +998,9 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, > if (pte_pfn(pte) == folio_end_pfn) > break; > > + if (any_writable) > + *any_writable |= writable; > + > expected_pte = pte_next_pfn(expected_pte); > ptep++; > } > @@ -1010,6 +1022,7 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma > { > struct page *page; > struct folio *folio; > + bool any_writable; > int err, nr; > > page = vm_normal_page(src_vma, addr, pte); > @@ -1024,7 +1037,8 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma > * by keeping the batching logic separate. > */ > if (unlikely(!*prealloc && folio_test_large(folio) && max_nr != 1)) { > - nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr); > + nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr, > + &any_writable); > if (folio_test_anon(folio)) { > folio_ref_add(folio, nr); > if (unlikely(folio_try_dup_anon_rmap_ptes(folio, page, > @@ -1039,6 +1053,8 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma > folio_dup_file_rmap_ptes(folio, page, nr); > rss[mm_counter_file(page)] += nr; > } > + if (any_writable) > + pte = pte_mkwrite(pte, src_vma); > __copy_present_ptes(dst_vma, src_vma, dst_pte, src_pte, pte, > addr, nr); > return nr;
diff --git a/mm/memory.c b/mm/memory.c index 341b2be845b6e..a26fd0669016b 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -955,7 +955,7 @@ static __always_inline void __copy_present_ptes(struct vm_area_struct *dst_vma, static inline pte_t __pte_batch_clear_ignored(pte_t pte) { - return pte_clear_soft_dirty(pte_mkclean(pte_mkold(pte))); + return pte_wrprotect(pte_clear_soft_dirty(pte_mkclean(pte_mkold(pte)))); } /* @@ -963,20 +963,29 @@ static inline pte_t __pte_batch_clear_ignored(pte_t pte) * pages of the same folio. * * All PTEs inside a PTE batch have the same PTE bits set, excluding the PFN. - * the accessed bit, dirty bit and soft-dirty bit. + * the accessed bit, dirty bit, soft-dirty bit and writable bit. + . If "any_writable" is set, it will indicate if any other PTE besides the + * first (given) PTE is writable. */ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, - pte_t *start_ptep, pte_t pte, int max_nr) + pte_t *start_ptep, pte_t pte, int max_nr, bool *any_writable) { unsigned long folio_end_pfn = folio_pfn(folio) + folio_nr_pages(folio); const pte_t *end_ptep = start_ptep + max_nr; pte_t expected_pte = __pte_batch_clear_ignored(pte_next_pfn(pte)); pte_t *ptep = start_ptep + 1; + bool writable; + + if (any_writable) + *any_writable = false; VM_WARN_ON_FOLIO(!pte_present(pte), folio); while (ptep != end_ptep) { - pte = __pte_batch_clear_ignored(ptep_get(ptep)); + pte = ptep_get(ptep); + if (any_writable) + writable = !!pte_write(pte); + pte = __pte_batch_clear_ignored(pte); if (!pte_same(pte, expected_pte)) break; @@ -989,6 +998,9 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, if (pte_pfn(pte) == folio_end_pfn) break; + if (any_writable) + *any_writable |= writable; + expected_pte = pte_next_pfn(expected_pte); ptep++; } @@ -1010,6 +1022,7 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma { struct page *page; struct folio *folio; + bool any_writable; int err, nr; page = vm_normal_page(src_vma, addr, pte); @@ -1024,7 +1037,8 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma * by keeping the batching logic separate. */ if (unlikely(!*prealloc && folio_test_large(folio) && max_nr != 1)) { - nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr); + nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr, + &any_writable); if (folio_test_anon(folio)) { folio_ref_add(folio, nr); if (unlikely(folio_try_dup_anon_rmap_ptes(folio, page, @@ -1039,6 +1053,8 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma folio_dup_file_rmap_ptes(folio, page, nr); rss[mm_counter_file(page)] += nr; } + if (any_writable) + pte = pte_mkwrite(pte, src_vma); __copy_present_ptes(dst_vma, src_vma, dst_pte, src_pte, pte, addr, nr); return nr;
... and conditionally return to the caller if any pte except the first one is writable. fork() has to make sure to properly write-protect in case any PTE is writable. Other users (e.g., page unmaping) won't care. Signed-off-by: David Hildenbrand <david@redhat.com> --- mm/memory.c | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-)