On 17/04/2024 15:14, Lance Yang wrote: > This patch optimizes lazyfreeing with PTE-mapped mTHP[1] > (Inspired by David Hildenbrand[2]). We aim to avoid unnecessary folio > splitting if the large folio is fully mapped within the target range. > > If a large folio is locked or shared, or if we fail to split it, we just > leave it in place and advance to the next PTE in the range. But note that > the behavior is changed; previously, any failure of this sort would cause > the entire operation to give up. As large folios become more common, > sticking to the old way could result in wasted opportunities. > > On an Intel I5 CPU, lazyfreeing a 1GiB VMA backed by PTE-mapped folios of > the same size results in the following runtimes for madvise(MADV_FREE) in > seconds (shorter is better): > > Folio Size | Old | New | Change > ------------------------------------------ > 4KiB | 0.590251 | 0.590259 | 0% > 16KiB | 2.990447 | 0.185655 | -94% > 32KiB | 2.547831 | 0.104870 | -95% > 64KiB | 2.457796 | 0.052812 | -97% > 128KiB | 2.281034 | 0.032777 | -99% > 256KiB | 2.230387 | 0.017496 | -99% > 512KiB | 2.189106 | 0.010781 | -99% > 1024KiB | 2.183949 | 0.007753 | -99% > 2048KiB | 0.002799 | 0.002804 | 0% > > [1] https://lkml.kernel.org/r/20231207161211.2374093-5-ryan.roberts@xxxxxxx > [2] https://lore.kernel.org/linux-mm/20240214204435.167852-1-david@xxxxxxxxxx > > Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx> LGTM! Reviewed-by: Ryan Roberts <ryan.roberts@xxxxxxx> > --- > mm/internal.h | 12 ++++- > mm/madvise.c | 141 ++++++++++++++++++++++++++++---------------------- > mm/memory.c | 4 +- > 3 files changed, 91 insertions(+), 66 deletions(-) > > diff --git a/mm/internal.h b/mm/internal.h > index c6483f73ec13..daa59cef85d7 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -134,6 +134,8 @@ static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags) > * first one is writable. > * @any_young: Optional pointer to indicate whether any entry except the > * first one is young. > + * @any_dirty: Optional pointer to indicate whether any entry except the > + * first one is dirty. > * > * Detect a PTE batch: consecutive (present) PTEs that map consecutive > * pages of the same large folio. > @@ -149,18 +151,20 @@ static inline pte_t __pte_batch_clear_ignored(pte_t pte, fpb_t flags) > */ > static inline int folio_pte_batch(struct folio *folio, unsigned long addr, > pte_t *start_ptep, pte_t pte, int max_nr, fpb_t flags, > - bool *any_writable, bool *any_young) > + bool *any_writable, bool *any_young, bool *any_dirty) > { > 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, *ptep; > - bool writable, young; > + bool writable, young, dirty; > int nr; > > if (any_writable) > *any_writable = false; > if (any_young) > *any_young = false; > + if (any_dirty) > + *any_dirty = false; > > VM_WARN_ON_FOLIO(!pte_present(pte), folio); > VM_WARN_ON_FOLIO(!folio_test_large(folio) || max_nr < 1, folio); > @@ -176,6 +180,8 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, > writable = !!pte_write(pte); > if (any_young) > young = !!pte_young(pte); > + if (any_dirty) > + dirty = !!pte_dirty(pte); > pte = __pte_batch_clear_ignored(pte, flags); > > if (!pte_same(pte, expected_pte)) > @@ -193,6 +199,8 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, > *any_writable |= writable; > if (any_young) > *any_young |= young; > + if (any_dirty) > + *any_dirty |= dirty; > > nr = pte_batch_hint(ptep, pte); > expected_pte = pte_advance_pfn(expected_pte, nr); > diff --git a/mm/madvise.c b/mm/madvise.c > index f5e3699e7b54..d6f1889d6308 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -321,6 +321,39 @@ static inline bool can_do_file_pageout(struct vm_area_struct *vma) > file_permission(vma->vm_file, MAY_WRITE) == 0; > } > > +static inline int madvise_folio_pte_batch(unsigned long addr, unsigned long end, > + struct folio *folio, pte_t *ptep, > + pte_t pte, bool *any_young, > + bool *any_dirty) > +{ > + int max_nr = (end - addr) / PAGE_SIZE; > + const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY; > + > + return folio_pte_batch(folio, addr, ptep, pte, max_nr, fpb_flags, NULL, > + any_young, any_dirty); > +} > + > +static inline bool madvise_pte_split_folio(struct mm_struct *mm, pmd_t *pmd, > + unsigned long addr, > + struct folio *folio, pte_t **pte, > + spinlock_t **ptl) > +{ > + int err; > + > + if (!folio_trylock(folio)) > + return false; > + > + folio_get(folio); > + pte_unmap_unlock(*pte, *ptl); > + err = split_folio(folio); > + folio_unlock(folio); > + folio_put(folio); > + > + *pte = pte_offset_map_lock(mm, pmd, addr, ptl); > + > + return err == 0; > +} > + > static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, > unsigned long addr, unsigned long end, > struct mm_walk *walk) > @@ -456,41 +489,30 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, > * next pte in the range. > */ > if (folio_test_large(folio)) { > - const fpb_t fpb_flags = FPB_IGNORE_DIRTY | > - FPB_IGNORE_SOFT_DIRTY; > - int max_nr = (end - addr) / PAGE_SIZE; > bool any_young; > > - nr = folio_pte_batch(folio, addr, pte, ptent, max_nr, > - fpb_flags, NULL, &any_young); > - if (any_young) > - ptent = pte_mkyoung(ptent); > + nr = madvise_folio_pte_batch(addr, end, folio, pte, > + ptent, &any_young, NULL); > > if (nr < folio_nr_pages(folio)) { > - int err; > - > if (folio_likely_mapped_shared(folio)) > continue; > if (pageout_anon_only_filter && !folio_test_anon(folio)) > continue; > - if (!folio_trylock(folio)) > - continue; > - folio_get(folio); > + > arch_leave_lazy_mmu_mode(); > - pte_unmap_unlock(start_pte, ptl); > - start_pte = NULL; > - err = split_folio(folio); > - folio_unlock(folio); > - folio_put(folio); > - start_pte = pte = > - pte_offset_map_lock(mm, pmd, addr, &ptl); > + if (madvise_pte_split_folio(mm, pmd, addr, > + folio, &start_pte, &ptl)) > + nr = 0; > if (!start_pte) > break; > + pte = start_pte; > arch_enter_lazy_mmu_mode(); > - if (!err) > - nr = 0; > continue; > } > + > + if (any_young) > + ptent = pte_mkyoung(ptent); > } > > /* > @@ -688,44 +710,48 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, > continue; > > /* > - * If pmd isn't transhuge but the folio is large and > - * is owned by only this process, split it and > - * deactivate all pages. > + * If we encounter a large folio, only split it if it is not > + * fully mapped within the range we are operating on. Otherwise > + * leave it as is so that it can be marked as lazyfree. If we > + * fail to split a folio, leave it in place and advance to the > + * next pte in the range. > */ > if (folio_test_large(folio)) { > - int err; > + bool any_young, any_dirty; > > - if (folio_likely_mapped_shared(folio)) > - break; > - if (!folio_trylock(folio)) > - break; > - folio_get(folio); > - arch_leave_lazy_mmu_mode(); > - pte_unmap_unlock(start_pte, ptl); > - start_pte = NULL; > - err = split_folio(folio); > - folio_unlock(folio); > - folio_put(folio); > - if (err) > - break; > - start_pte = pte = > - pte_offset_map_lock(mm, pmd, addr, &ptl); > - if (!start_pte) > - break; > - arch_enter_lazy_mmu_mode(); > - pte--; > - addr -= PAGE_SIZE; > - continue; > + nr = madvise_folio_pte_batch(addr, end, folio, pte, > + ptent, &any_young, &any_dirty); > + > + if (nr < folio_nr_pages(folio)) { > + if (folio_likely_mapped_shared(folio)) > + continue; > + > + arch_leave_lazy_mmu_mode(); > + if (madvise_pte_split_folio(mm, pmd, addr, > + folio, &start_pte, &ptl)) > + nr = 0; > + if (!start_pte) > + break; > + pte = start_pte; > + arch_enter_lazy_mmu_mode(); > + continue; > + } > + > + if (any_young) > + ptent = pte_mkyoung(ptent); > + if (any_dirty) > + ptent = pte_mkdirty(ptent); > } > > if (folio_test_swapcache(folio) || folio_test_dirty(folio)) { > if (!folio_trylock(folio)) > continue; > /* > - * If folio is shared with others, we mustn't clear > - * the folio's dirty flag. > + * If we have a large folio at this point, we know it is > + * fully mapped so if its mapcount is the same as its > + * number of pages, it must be exclusive. > */ > - if (folio_mapcount(folio) != 1) { > + if (folio_mapcount(folio) != folio_nr_pages(folio)) { > folio_unlock(folio); > continue; > } > @@ -741,19 +767,10 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, > } > > if (pte_young(ptent) || pte_dirty(ptent)) { > - /* > - * Some of architecture(ex, PPC) don't update TLB > - * with set_pte_at and tlb_remove_tlb_entry so for > - * the portability, remap the pte with old|clean > - * after pte clearing. > - */ > - ptent = ptep_get_and_clear_full(mm, addr, pte, > - tlb->fullmm); > - > - ptent = pte_mkold(ptent); > - ptent = pte_mkclean(ptent); > - set_pte_at(mm, addr, pte, ptent); > - tlb_remove_tlb_entry(tlb, pte, addr); > + clear_young_dirty_ptes(vma, addr, pte, nr, > + CYDP_CLEAR_YOUNG | > + CYDP_CLEAR_DIRTY); > + tlb_remove_tlb_entries(tlb, pte, nr, addr); > } > folio_mark_lazyfree(folio); > } > diff --git a/mm/memory.c b/mm/memory.c > index 33d87b64d15d..9e07d1b9020c 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -989,7 +989,7 @@ copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma > flags |= FPB_IGNORE_SOFT_DIRTY; > > nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr, flags, > - &any_writable, NULL); > + &any_writable, NULL, NULL); > folio_ref_add(folio, nr); > if (folio_test_anon(folio)) { > if (unlikely(folio_try_dup_anon_rmap_ptes(folio, page, > @@ -1558,7 +1558,7 @@ static inline int zap_present_ptes(struct mmu_gather *tlb, > */ > if (unlikely(folio_test_large(folio) && max_nr != 1)) { > nr = folio_pte_batch(folio, addr, pte, ptent, max_nr, fpb_flags, > - NULL, NULL); > + NULL, NULL, NULL); > > zap_present_folio_ptes(tlb, vma, folio, page, pte, ptent, nr, > addr, details, rss, force_flush,
