Hi Lance, Thanks for working on this! On 25/02/2024 12:32, Lance Yang wrote: > This patch improves madvise_free_pte_range() to correctly > handle large folio that is smaller than PMD-size When you say "correctly handle" are you implying there is a bug with the current implementation or are you just saying you can optimize this to improve performance? I'm not convinced there is a bug, but I agree there is certainly room for performance improvement. Thanks, Ryan > (for example, 16KiB to 1024KiB[1]). It’s probably part of > the preparation to support anonymous multi-size THP. > > Additionally, when the consecutive PTEs are mapped to > consecutive pages of the same large folio (mTHP), if the > folio is locked before madvise(MADV_FREE) or cannot be > split, then all subsequent PTEs within the same PMD will > be skipped. However, they should have been MADV_FREEed. > > Moreover, this patch also optimizes lazyfreeing with > PTE-mapped mTHP (Inspired by David Hildenbrand[2]). We > aim to avoid unnecessary folio splitting if the large > folio is entirely within the given range. > > 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 | 0.590264 | 0% > 16KiB | 2.990447 | 0.182167 | -94% > 32KiB | 2.547831 | 0.101622 | -96% > 64KiB | 2.457796 | 0.049726 | -98% > 128KiB | 2.281034 | 0.030109 | -99% > 256KiB | 2.230387 | 0.015838 | -99% > 512KiB | 2.189106 | 0.009149 | -99% > 1024KiB | 2.183949 | 0.006620 | -99% > 2048KiB | 0.002799 | 0.002795 | 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> > --- > mm/madvise.c | 69 +++++++++++++++++++++++++++++++++++++++++++--------- > 1 file changed, 58 insertions(+), 11 deletions(-) > > diff --git a/mm/madvise.c b/mm/madvise.c > index cfa5e7288261..bcbf56595a2e 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -676,11 +676,43 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, > */ > if (folio_test_large(folio)) { > int err; > + unsigned long next_addr, align; > > - if (folio_estimated_sharers(folio) != 1) > - break; > - if (!folio_trylock(folio)) > - break; > + if (folio_estimated_sharers(folio) != 1 || > + !folio_trylock(folio)) > + goto skip_large_folio; > + > + align = folio_nr_pages(folio) * PAGE_SIZE; > + next_addr = ALIGN_DOWN(addr + align, align); > + > + /* > + * If we mark only the subpages as lazyfree, > + * split the large folio. > + */ > + if (next_addr > end || next_addr - addr != align) > + goto split_large_folio; > + > + /* > + * Avoid unnecessary folio splitting if the large > + * folio is entirely within the given range. > + */ > + folio_test_clear_dirty(folio); > + folio_unlock(folio); > + for (; addr != next_addr; pte++, addr += PAGE_SIZE) { > + ptent = ptep_get(pte); > + if (pte_young(ptent) || pte_dirty(ptent)) { > + 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); > + } > + } > + folio_mark_lazyfree(folio); > + goto next_folio; > + > +split_large_folio: > folio_get(folio); > arch_leave_lazy_mmu_mode(); > pte_unmap_unlock(start_pte, ptl); > @@ -688,13 +720,28 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, > 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(); > + > + /* > + * If the large folio is locked before madvise(MADV_FREE) > + * or cannot be split, we just skip it. > + */ > + if (err) { > +skip_large_folio: > + if (next_addr >= end) > + break; > + pte += (next_addr - addr) / PAGE_SIZE; > + addr = next_addr; > + } > + > + if (!start_pte) { > + start_pte = pte = pte_offset_map_lock( > + mm, pmd, addr, &ptl); > + if (!start_pte) > + break; > + arch_enter_lazy_mmu_mode(); > + } > + > +next_folio: > pte--; > addr -= PAGE_SIZE; > continue;
