Commit 4a34c584 authored by Dev Jain's avatar Dev Jain Committed by Andrew Morton
Browse files

mempolicy: optimize queue_folios_pte_range by PTE batching 

After the check for queue_folio_required(), the code only cares about the
folio in the for loop, i.e the PTEs are redundant.  Therefore, optimize
this loop by skipping over a PTE batch mapping the same folio.

With a test program migrating pages of the calling process, which includes
a mapped VMA of size 4GB with pte-mapped large folios of order-9, and
migrating once back and forth node-0 and node-1, the average execution
time reduces from 7.5 to 4 seconds, giving an approx 47% speedup.

Link: https://lkml.kernel.org/r/20250416053048.96479-1-dev.jain@arm.com


Signed-off-by: default avatarDev Jain <dev.jain@arm.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Yang Shi <yang@os.amperecomputing.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 75404e07

mm/mempolicy.c

+10 −2
Original line number Diff line number Diff line
@@ -566,6 +566,7 @@ static void queue_folios_pmd(pmd_t *pmd, struct mm_walk *walk) 
static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr,

			unsigned long end, struct mm_walk *walk)

{

	const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;

	struct vm_area_struct *vma = walk->vma;

	struct folio *folio;

	struct queue_pages *qp = walk->private;
@@ -573,6 +574,7 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr, 
	pte_t *pte, *mapped_pte;

	pte_t ptent;

	spinlock_t *ptl;

	int max_nr, nr;



	ptl = pmd_trans_huge_lock(pmd, vma);

	if (ptl) {
@@ -586,7 +588,9 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr, 
		walk->action = ACTION_AGAIN;

		return 0;

	}

	for (; addr != end; pte++, addr += PAGE_SIZE) {

	for (; addr != end; pte += nr, addr += nr * PAGE_SIZE) {

		max_nr = (end - addr) >> PAGE_SHIFT;

		nr = 1;

		ptent = ptep_get(pte);

		if (pte_none(ptent))

			continue;
@@ -598,6 +602,10 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr, 
		folio = vm_normal_folio(vma, addr, ptent);

		if (!folio || folio_is_zone_device(folio))

			continue;

		if (folio_test_large(folio) && max_nr != 1)

			nr = folio_pte_batch(folio, addr, pte, ptent,

					     max_nr, fpb_flags,

					     NULL, NULL, NULL);

		/*

		 * vm_normal_folio() filters out zero pages, but there might

		 * still be reserved folios to skip, perhaps in a VDSO.
@@ -630,7 +638,7 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr, 
		if (!(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) ||

		    !vma_migratable(vma) ||

		    !migrate_folio_add(folio, qp->pagelist, flags)) {

			qp->nr_failed++;

			qp->nr_failed += nr;

			if (strictly_unmovable(flags))

				break;

		}