Hey Ryan, Thanks for taking time to review! On Thu, Apr 4, 2024 at 1:35 AM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: > > On 02/04/2024 13:40, 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% > > I'm guessing the reason that 2M is not showing any change is because its > PMD-mapped and splitting is already elided? If you were to force it to be Your guess is correct. The lack of change in 2M is because it's PMD-mapped. > PTE-mapped then you'll see the very impressive speed-up there too. Don't worry > about doing that on my account though; these results are already sufficient IMHO. > > > > > [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> > > --- > > mm/internal.h | 12 ++++- > > mm/madvise.c | 147 ++++++++++++++++++++++++++------------------------ > > mm/memory.c | 4 +- > > 3 files changed, 88 insertions(+), 75 deletions(-) > > > > diff --git a/mm/internal.h b/mm/internal.h > > index 3df06a152ff0..cdc6e2162b30 100644 > > --- a/mm/internal.h > > +++ b/mm/internal.h > > @@ -132,6 +132,8 @@ 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. > > @@ -147,18 +149,20 @@ 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); > > @@ -174,6 +178,8 @@ 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)) > > @@ -191,6 +197,8 @@ 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 bd00b83e7c50..8197effd9f14 100644 > > --- a/mm/madvise.c > > +++ b/mm/madvise.c > > @@ -321,6 +321,38 @@ 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 *pte, > > + bool *any_writable, bool *any_young, bool *any_dirty) > > any_writable is always NULL. Do you need it? Thanks for pointing that out. It seems that the any_writable parameter is redundant here, so I'll drop it. > > > +{ > > + 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, pte, ptep_get(pte), max_nr, > > ptep_get() was problematic for performance of the order-0 folio case when we > batched fork(). So we are deliberately passing around the value we already read > in the main loop. Granted this case is not so performance critical because we > only end up here for large folios. But I would still prefer to just pass the > data we have already read into this function rather than reading it again. Thanks for the explanation! I completely agree. I‘ll pass the data we’ve already read into this function. > > > + fpb_flags, any_writable, 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, > > nit: I know 80 chars is a soft limit now (and I think 100 is a hard limit), but > try to be consistent. You could move the addr param to the previous line and be > within the 100 char limit. Personally I would just make the prototype fit in 80 > chars (same goes for madvise_folio_pte_batch). Got it. Thanks. > > > + spinlock_t **ptl) > > +{ > > + int err; > > + > > + if (!folio_trylock(folio)) > > + return false; > > + > > + folio_get(folio); > > + pte_unmap_unlock(*pte, *ptl); > > + *pte = NULL; > > nit: you don't need this since you are later unconditionally setting it again. Nice. I'll remove it. > > > + 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) > > @@ -456,40 +488,26 @@ 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); > > + nr = madvise_folio_pte_batch(addr, end, folio, pte, > > + NULL, &any_young, NULL); > > if (any_young) > > ptent = pte_mkyoung(ptent); > > > > 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); > > - if (err) > > - continue; > > - 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(); > > - nr = 0; > > continue; > > This change fixes a bug I've introduced in my swap-out series. Nice. I tried to > fix in v6, but looking at this, I've realised its still broken. I've replied > against that series with the fix. > > > > } > > } > > @@ -688,72 +706,59 @@ 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; > > + nr = madvise_folio_pte_batch(addr, end, folio, pte, > > + NULL, &any_young, &any_dirty); > > + if (any_young || any_dirty) > > + ptent = pte_mkdirty(pte_mkyoung(ptent)); > > I don't think it makes any difference to how ptent is consumed below, but its > probably more intuitive to separate these two operations: > > if (any_young) > ptent = pte_mkyoung(ptent); > if (any_dirty) > ptent = pte_mkdirty(ptent); I agree that it's more intuitive to separate these two operations. Thanks. > > > > > - 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; > > - } > > + if (nr < folio_nr_pages(folio)) { > > + if (folio_likely_mapped_shared(folio)) > > + continue; > > > > - 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 (folio_mapcount(folio) != 1) { > > - folio_unlock(folio); > > + 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 (!folio_trylock(folio)) > > + continue; > > + /* > > + * 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) != folio_nr_pages(folio)) { > > + folio_unlock(folio); > > + continue; > > + } > > + if (folio_test_swapcache(folio) || folio_test_dirty(folio)) { > > I don't understand the rationale for reducing the scope of this conditional? > Previously it was used to avoid having to lock the folio if it wasn't in the > swapcache or if it wasn't dirty. So now you will be locking much more often. You're right. I should keep the previous behavior of avoiding locking the folio if wasn't in the swapcache or if it wasn't dirty. Thanks again for your time! Lance > > Thanks, > Ryan > > > if (folio_test_swapcache(folio) && > > !folio_free_swap(folio)) { > > folio_unlock(folio); > > continue; > > } > > - > > folio_clear_dirty(folio); > > - folio_unlock(folio); > > } > > + folio_unlock(folio); > > > > 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); > > + mkold_clean_ptes(vma, addr, pte, nr, tlb->fullmm); > > + tlb_remove_tlb_entries(tlb, pte, nr, addr); > > } > > folio_mark_lazyfree(folio); > > } > > diff --git a/mm/memory.c b/mm/memory.c > > index 912cd738ec03..24769ecb59e5 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, > > @@ -1559,7 +1559,7 @@ 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, >
