On Mon, Sep 16, 2024 at 11:08 PM Dev Jain <dev.jain@xxxxxxx> wrote: > > For an mTHP allocation, we need to check, for every order, whether for > that order, we have enough number of contiguous PTEs empty. Instead of > iterating the while loop for every order, use some information, which > is the first set PTE found, from the previous iteration to eliminate > some cases. The key to understanding the correctness of the patch > is that the ranges we want to examine form a strictly decreasing > sequence of nested intervals. Could we include some benchmark data here, as suggested by Ryan in this thread? https://lore.kernel.org/linux-mm/58f91a56-890a-45d0-8b1f-47c4c70c9600@xxxxxxx/ > > Suggested-by: Ryan Roberts <ryan.roberts@xxxxxxx> > Signed-off-by: Dev Jain <dev.jain@xxxxxxx> > --- > mm/memory.c | 20 ++++++++++++++++++-- > 1 file changed, 18 insertions(+), 2 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 8bb1236de93c..e81c6abe09ce 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4633,10 +4633,11 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf) > { > struct vm_area_struct *vma = vmf->vma; > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > + pte_t *first_set_pte = NULL, *align_pte, *pte; > unsigned long orders; > struct folio *folio; > unsigned long addr; > - pte_t *pte; > + int max_empty; > gfp_t gfp; > int order; > > @@ -4671,8 +4672,23 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf) > order = highest_order(orders); > while (orders) { > addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order); > - if (pte_range_none(pte + pte_index(addr), 1 << order) == 1 << order) > + align_pte = pte + pte_index(addr); > + > + /* Range to be scanned known to be empty */ > + if (align_pte + (1 << order) <= first_set_pte) > + break; > + > + /* Range to be scanned contains first_set_pte */ > + if (align_pte <= first_set_pte) > + goto repeat; > + > + /* align_pte > first_set_pte, so need to check properly */ > + max_empty = pte_range_none(align_pte, 1 << order); > + if (max_empty == 1 << order) > break; > + > + first_set_pte = align_pte + max_empty; > +repeat: > order = next_order(&orders, order); > } > > -- > 2.30.2 > Thanks barry
