Hey Ryan, Thanks for taking time to review! On Mon, Feb 26, 2024 at 9:00 PM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: > > 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. I agree with your point, and will update the changelog in v2. Thanks again for your time! Best, Lance > > 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; >
