[PATCH v2 15/17] mm/damon: handle device-exclusive entries correctly in damon_folio_mkold_one()
From: David Hildenbrand <hidden>
Date: 2025-02-10 19:39:05
Also in:
damon, dri-devel, linux-doc, linux-mm, linux-perf-users, lkml, nouveau
Subsystem:
damon, memory management, the rest · Maintainers:
SeongJae Park, Andrew Morton, Linus Torvalds
Ever since commit b756a3b5e7ea ("mm: device exclusive memory access")
we can return with a device-exclusive entry from page_vma_mapped_walk().
damon_folio_mkold_one() is not prepared for that and calls
damon_ptep_mkold() with PFN swap PTEs. Teach damon_ptep_mkold() to deal
with these PFN swap PTEs. Note that device-private entries are so far not
applicable on that path, as damon_get_folio() filters out non-lru
folios.
Should we just skip PFN swap PTEs completely? Possible, but it seems
straight forward to just handle it correctly.
Note that we could currently only run into this case with
device-exclusive entries on THPs. We still adjust the mapcount on
conversion to device-exclusive; this makes the rmap walk
abort early for small folios, because we'll always have
!folio_mapped() with a single device-exclusive entry. We'll adjust the
mapcount logic once all page_vma_mapped_walk() users can properly
handle device-exclusive entries.
Signed-off-by: David Hildenbrand <redacted>
---
mm/damon/ops-common.c | 23 +++++++++++++++++++++--
1 file changed, 21 insertions(+), 2 deletions(-)
diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c
index d25d99cb5f2bb..86a50e8fbc806 100644
--- a/mm/damon/ops-common.c
+++ b/mm/damon/ops-common.c@@ -9,6 +9,8 @@ #include <linux/page_idle.h> #include <linux/pagemap.h> #include <linux/rmap.h> +#include <linux/swap.h> +#include <linux/swapops.h> #include "ops-common.h"
@@ -39,12 +41,29 @@ struct folio *damon_get_folio(unsigned long pfn) void damon_ptep_mkold(pte_t *pte, struct vm_area_struct *vma, unsigned long addr) { - struct folio *folio = damon_get_folio(pte_pfn(ptep_get(pte))); + pte_t pteval = ptep_get(pte); + struct folio *folio; + bool young = false; + unsigned long pfn; + + if (likely(pte_present(pteval))) + pfn = pte_pfn(pteval); + else + pfn = swp_offset_pfn(pte_to_swp_entry(pteval)); + folio = damon_get_folio(pfn); if (!folio) return; - if (ptep_clear_young_notify(vma, addr, pte)) + /* + * PFN swap PTEs, such as device-exclusive ones, that actually map pages + * are "old" from a CPU perspective. The MMU notifier takes care of any + * device aspects. + */ + if (likely(pte_present(pteval))) + young |= ptep_test_and_clear_young(vma, addr, pte); + young |= mmu_notifier_clear_young(vma->vm_mm, addr, addr + PAGE_SIZE); + if (young) folio_set_young(folio); folio_set_idle(folio);
--
2.48.1