Re: [PATCH 1/1] mm/mlock: implement folio_mlock_step() using folio_pte_batch()

From: Baolin Wang
Date: Mon Jun 03 2024 - 04:59:19 EST




On 2024/6/3 12:14, Barry Song wrote:
On Mon, Jun 3, 2024 at 3:31 PM Lance Yang <ioworker0@xxxxxxxxx> wrote:

Let's make folio_mlock_step() simply a wrapper around folio_pte_batch(),
which will greatly reduce the cost of ptep_get() when scanning a range of
contptes.

Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx>
---
mm/mlock.c | 23 ++++++-----------------
1 file changed, 6 insertions(+), 17 deletions(-)

diff --git a/mm/mlock.c b/mm/mlock.c
index 30b51cdea89d..1ae6232d38cf 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -307,26 +307,15 @@ void munlock_folio(struct folio *folio)
static inline unsigned int folio_mlock_step(struct folio *folio,
pte_t *pte, unsigned long addr, unsigned long end)
{
- unsigned int count, i, nr = folio_nr_pages(folio);
- unsigned long pfn = folio_pfn(folio);
- pte_t ptent = ptep_get(pte);
-
- if (!folio_test_large(folio))
+ if (likely(!folio_test_large(folio)))
return 1;

- count = pfn + nr - pte_pfn(ptent);
- count = min_t(unsigned int, count, (end - addr) >> PAGE_SHIFT);
-
- for (i = 0; i < count; i++, pte++) {
- pte_t entry = ptep_get(pte);
-
- if (!pte_present(entry))
- break;
- if (pte_pfn(entry) - pfn >= nr)
- break;
- }
+ const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
+ int max_nr = (end - addr) / PAGE_SIZE;
+ pte_t ptent = ptep_get(pte);

- return i;
+ return folio_pte_batch(folio, addr, pte, ptent, max_nr, fpb_flags, NULL,
+ NULL, NULL);
}

what about a minimum change as below?
index 30b51cdea89d..e8b98f84fbd2 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -307,26 +307,15 @@ void munlock_folio(struct folio *folio)
static inline unsigned int folio_mlock_step(struct folio *folio,
pte_t *pte, unsigned long addr, unsigned long end)
{
- unsigned int count, i, nr = folio_nr_pages(folio);
- unsigned long pfn = folio_pfn(folio);
+ unsigned int count = (end - addr) >> PAGE_SHIFT;
pte_t ptent = ptep_get(pte);
+ const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;

if (!folio_test_large(folio))
return 1;

- count = pfn + nr - pte_pfn(ptent);
- count = min_t(unsigned int, count, (end - addr) >> PAGE_SHIFT);
-
- for (i = 0; i < count; i++, pte++) {
- pte_t entry = ptep_get(pte);
-
- if (!pte_present(entry))
- break;
- if (pte_pfn(entry) - pfn >= nr)
- break;
- }
-
- return i;
+ return folio_pte_batch(folio, addr, pte, ptent, count, fpb_flags, NULL,
+ NULL, NULL);
}

LGTM.
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>