Re: [PATCH v13 08/14] mm: multi-gen LRU: support page table walks

[Yu Zhao]

On Wed, Jul 06, 2022 at 04:00:17PM -0600, Yu Zhao wrote:

...

> +/*
> + * Some userspace memory allocators map many single-page VMAs. Instead of
> + * returning back to the PGD table for each of such VMAs, finish an entire PMD
> + * table to reduce zigzags and improve cache performance.
> + */
> +static bool get_next_vma(unsigned long mask, unsigned long size, struct mm_walk *args,
> +			 unsigned long *vm_start, unsigned long *vm_end)
> +{
> +	unsigned long start = round_up(*vm_end, size);
> +	unsigned long end = (start | ~mask) + 1;
> +
> +	VM_WARN_ON_ONCE(mask & size);
> +	VM_WARN_ON_ONCE((start & mask) != (*vm_start & mask));
> +
> +	while (args->vma) {
> +		if (start >= args->vma->vm_end) {
> +			args->vma = args->vma->vm_next;
> +			continue;
> +		}
> +
> +		if (end && end <= args->vma->vm_start)
> +			return false;
> +
> +		if (should_skip_vma(args->vma->vm_start, args->vma->vm_end, args)) {
> +			args->vma = args->vma->vm_next;
> +			continue;
> +		}
> +
> +		*vm_start = max(start, args->vma->vm_start);
> +		*vm_end = min(end - 1, args->vma->vm_end - 1) + 1;
> +
> +		return true;
> +	}
> +
> +	return false;
> +}

To make the above work on top of the Maple Tree:

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7096ff7836db..c0c1195da803 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3689,23 +3689,14 @@ static bool get_next_vma(unsigned long mask, unsigned long size, struct mm_walk
 {
 	unsigned long start = round_up(*vm_end, size);
 	unsigned long end = (start | ~mask) + 1;
+	VMA_ITERATOR(vmi, args->mm, start);
 
 	VM_WARN_ON_ONCE(mask & size);
 	VM_WARN_ON_ONCE((start & mask) != (*vm_start & mask));
 
-	while (args->vma) {
-		if (start >= args->vma->vm_end) {
-			args->vma = args->vma->vm_next;
+	for_each_vma_range(vmi, args->vma, end) {
+		if (should_skip_vma(args->vma->vm_start, args->vma->vm_end, args))
 			continue;
-		}
-
-		if (end && end <= args->vma->vm_start)
-			return false;
-
-		if (should_skip_vma(args->vma->vm_start, args->vma->vm_end, args)) {
-			args->vma = args->vma->vm_next;
-			continue;
-		}
 
 		*vm_start = max(start, args->vma->vm_start);
 		*vm_end = min(end - 1, args->vma->vm_end - 1) + 1;