Messages in this thread | | | Date | Thu, 18 Apr 2024 14:03:05 +0200 | Subject | Re: [PATCH v9 4/4] mm/madvise: optimize lazyfreeing with mTHP in madvise_free | From | David Hildenbrand <> |
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On 18.04.24 12:57, 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@arm.com > [2] https://lore.kernel.org/linux-mm/20240214204435.167852-1-david@redhat.com > > Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> > Signed-off-by: Lance Yang <ioworker0@gmail.com> > --- > mm/madvise.c | 85 +++++++++++++++++++++++++++------------------------- > 1 file changed, 44 insertions(+), 41 deletions(-) > > diff --git a/mm/madvise.c b/mm/madvise.c > index 4597a3568e7e..375ab3234603 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -643,6 +643,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, > unsigned long end, struct mm_walk *walk) > > { > + const cydp_t cydp_flags = CYDP_CLEAR_YOUNG | CYDP_CLEAR_DIRTY; > struct mmu_gather *tlb = walk->private; > struct mm_struct *mm = tlb->mm; > struct vm_area_struct *vma = walk->vma; > @@ -697,44 +698,57 @@ 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, NULL); > + > + if (nr < folio_nr_pages(folio)) { > + int err; > + > + if (folio_likely_mapped_shared(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);
I'd just put it on a single line.
> + if (!start_pte) > + break; > + arch_enter_lazy_mmu_mode(); > + if (!err) > + nr = 0; > + continue; > + } > + > + if (any_young) > + ptent = pte_mkyoung(ptent); > + if (any_dirty)
any_dirty is never set, likely missed to pass it to madvise_folio_pte_batch().
Apart from that LGTM and this patch is much easier to review now!
With above:
Acked-by: David Hildenbrand <david@redhat.com>
-- Cheers,
David / dhildenb
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