On 2026/7/9 19:25, Li Zhe wrote:
memmap_init_zone_device() currently mixes refcount policy and core
ZONE_DEVICE page setup in a single helper.
Factor the refcount-reset predicate into pagemap_resets_refcount(), move
the common page initialization into __zone_device_page_init(), and wrap
the existing slow path in zone_device_page_init_slow().
Hi,
Sorry if this has been discussed before, but I'm still curious—what
is the significance of the 'slow' suffix here? I don't think I quite
understand why this is called the 'slow path' here. Is there also a
'fast path' for initializing struct page?
Thanks.
This keeps the slow-path behaviour unchanged and gives later patches
reusable helper boundaries.
No functional change intended.
Signed-off-by: Li Zhe <[email protected]>
Reviewed-by: Mike Rapoport (Microsoft) <[email protected]>
---
mm/mm_init.c | 56 ++++++++++++++++++++++++++++++++++------------------
1 file changed, 37 insertions(+), 19 deletions(-)
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 95808ab5cfdb..5fccfbacf855 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1005,11 +1005,37 @@ static void __init memmap_init(void)
}
#ifdef CONFIG_ZONE_DEVICE
-static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
+/*
+ * Return true when the free path for this pagemap type restores the page
+ * refcount to 1, so memmap_init_zone_device() can keep the count set by
+ * __init_single_page(). Otherwise initialize the refcount to 0 and leave
+ * it to the allocator or pgmap callbacks to raise it when the page is
+ * handed out again.
+ */
+static inline bool pagemap_resets_refcount(const struct dev_pagemap *pgmap)
+{
+ /*
+ * MEMORY_DEVICE_GENERIC pages regain a refcount of 1 in the free
+ * path. The remaining ZONE_DEVICE types start from 0 here and raise
+ * the count again when the allocator or driver hands the page out.
+ */
+ switch (pgmap->type) {
+ case MEMORY_DEVICE_FS_DAX:
+ case MEMORY_DEVICE_PRIVATE:
+ case MEMORY_DEVICE_COHERENT:
+ case MEMORY_DEVICE_PCI_P2PDMA:
+ return false;
+ case MEMORY_DEVICE_GENERIC:
+ return true;
+ }
+
+ return true;
+}
+
+static void __ref __zone_device_page_init(struct page *page, unsigned long pfn,
unsigned long zone_idx, int nid,
struct dev_pagemap *pgmap)
{
-
__init_single_page(page, pfn, zone_idx, nid);
/*
@@ -1028,23 +1054,15 @@ static void __ref __init_zone_device_page(struct page
*page, unsigned long pfn,
*/
page_folio(page)->pgmap = pgmap;
page->zone_device_data = NULL;
+}
- /*
- * MEMORY_DEVICE_GENERIC pages regain a refcount of 1 in the free
- * path. The remaining ZONE_DEVICE types start from 0 here and raise
- * the count again when the allocator or driver hands the page out.
- */
- switch (pgmap->type) {
- case MEMORY_DEVICE_FS_DAX:
- case MEMORY_DEVICE_PRIVATE:
- case MEMORY_DEVICE_COHERENT:
- case MEMORY_DEVICE_PCI_P2PDMA:
+static void __ref zone_device_page_init_slow(struct page *page,
+ unsigned long pfn, unsigned long zone_idx, int nid,
+ struct dev_pagemap *pgmap)
+{
+ __zone_device_page_init(page, pfn, zone_idx, nid, pgmap);
+ if (!pagemap_resets_refcount(pgmap))
set_page_count(page, 0);
- break;
-
- case MEMORY_DEVICE_GENERIC:
- break;
- }
}
/*
@@ -1090,7 +1108,7 @@ static void __ref memmap_init_compound(struct page *head,
for (pfn = head_pfn + 1; pfn < end_pfn; pfn++) {
struct page *page = pfn_to_page(pfn);
- __init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
+ zone_device_page_init_slow(page, pfn, zone_idx, nid, pgmap);
prep_compound_tail(page, head, order);
set_page_count(page, 0);
}
@@ -1126,7 +1144,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
for (pfn = start_pfn; pfn < end_pfn; pfn += pfns_per_compound) {
struct page *page = pfn_to_page(pfn);
- __init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
+ zone_device_page_init_slow(page, pfn, zone_idx, nid, pgmap);
if (IS_ALIGNED(pfn, PAGES_PER_SECTION))
cond_resched();
--
2.20.1
