On Thu, Apr 18, 2024 at 8:44 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > > On 18.04.24 14:33, Lance Yang wrote: > > On Thu, Apr 18, 2024 at 8:03 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > >> > >> 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@xxxxxxx > >>> [2] https://lore.kernel.org/linux-mm/20240214204435.167852-1-david@xxxxxxxxxx > >>> > >>> Reviewed-by: Ryan Roberts <ryan.roberts@xxxxxxx> > >>> Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx> > >>> --- > >>> 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. > > > > start_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl); > > > > I suddenly realized that putting it on a single line would exceed the > > 80-char limit. > > Which is fine according to Documentation/process/coding-style.rst > > ... as long as it aids readability. > > Alternatively, the following might do: > > pte = pte_offset_map_lock(mm, pmd, addr, &ptl); > start_pte = pte; Yep, I understood. Thanks, Lance > > -- > Cheers, > > David / dhildenb >
