Hey David, Thanks a lot for taking time to review! On Thu, Apr 18, 2024 at 1:05 AM David Hildenbrand <david@xxxxxxxxxx> wrote: > > On 17.04.24 16:14, 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> > > Some of the changes could have been moved into separate patches to ease > review ;) > > At least the folio_pte_batch() change and factoring out some stuff from > madvise_cold_or_pageout_pte_range(). But see below on the latter. Thanks for your suggestion! It makes sense to split some of the changes into separate patches for easier review :) > > > --- > > mm/internal.h | 12 ++++- > > mm/madvise.c | 141 ++++++++++++++++++++++++++++---------------------- > > mm/memory.c | 4 +- > > 3 files changed, 91 insertions(+), 66 deletions(-) > > [...] > > > 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; > > Reverse Christmas tree looks nicer ;) Yep, I understand. > > > + > > + 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); > > Staring at this helper again, I am really not sure if we should have it. > Calling semantics are "special" and that pte_t **pte is just ... > "special" as well ;) > > Can we just leave that part as is, in the caller? That would also mean > less madvise_cold_or_pageout_pte_range() churn ... which i would welcome > as part of this patch. Yep, let's leave that part as it is in the caller :) > > [...] > > > @@ -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); > > That indent looks odd. I suggest simply having a local variable > > const cydp_t cydp_flags = CYDP_CLEAR_YOUNG | CYDP_CLEAR_DIRTY; > > and then use cydp_flags here that will make this easier to read. Nice. I'll use cydp_flags here in the next version. Thanks again for the review! Lance > > -- > Cheers, > > David / dhildenb >
