[PATCH v1 06/11] mm/ksm: convert scan_get_next_rmap_item() from follow_page() to folio_walk

David Hildenbrand
2024-08-02T15:56:20Z

Let's use folio_walk instead, for example avoiding taking temporary
folio references if the folio does obviously not even apply and getting
rid of one more follow_page() user. We cannot move all handling under the
PTL, so leave the rmap handling (which implies an allocation) out.

Note that zeropages obviously don't apply: old code could just have
specified FOLL_DUMP. Further, we don't care about losing the secretmem
check in follow_page(): these are never anon pages and
vma_ksm_compatible() would never consider secretmem vmas
(VM_SHARED | VM_MAYSHARE must be set for secretmem, see secretmem_mmap()).

Signed-off-by: David Hildenbrand <david@redhat.com>
---
mm/ksm.c | 38 ++++++++++++++++++++++++--------------
1 file changed, 24 insertions(+), 14 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 742b005f3f77..0f5b2bba4ef0 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2564,36 +2564,46 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
ksm_scan.address = vma->vm_end;

while (ksm_scan.address < vma->vm_end) {
+ struct page *tmp_page = NULL;
+ struct folio_walk fw;
+ struct folio *folio;
+
if (ksm_test_exit(mm))
break;
- *page = follow_page(vma, ksm_scan.address, FOLL_GET);
- if (IS_ERR_OR_NULL(*page)) {
- ksm_scan.address += PAGE_SIZE;
- cond_resched();
- continue;
+
+ folio = folio_walk_start(&fw, vma, ksm_scan.address, 0);
+ if (folio) {
+ if (!folio_is_zone_device(folio) &&
+ folio_test_anon(folio)) {
+ folio_get(folio);
+ tmp_page = fw.page;
+ }
+ folio_walk_end(&fw, vma);
}
- if (is_zone_device_page(*page))
- goto next_page;
- if (PageAnon(*page)) {
- flush_anon_page(vma, *page, ksm_scan.address);
- flush_dcache_page(*page);
+
+ if (tmp_page) {
+ flush_anon_page(vma, tmp_page, ksm_scan.address);
+ flush_dcache_page(tmp_page);
rmap_item = get_next_rmap_item(mm_slot,
ksm_scan.rmap_list, ksm_scan.address);
if (rmap_item) {
ksm_scan.rmap_list =
&rmap_item->rmap_list;

- if (should_skip_rmap_item(*page, rmap_item))
+ if (should_skip_rmap_item(tmp_page, rmap_item)) {
+ folio_put(folio);
goto next_page;
+ }

ksm_scan.address += PAGE_SIZE;
- } else
- put_page(*page);
+ *page = tmp_page;
+ } else {
+ folio_put(folio);
+ }
mmap_read_unlock(mm);
return rmap_item;
}
next_page:
- put_page(*page);
ksm_scan.address += PAGE_SIZE;
cond_resched();
}
--
2.45.2