On 13.12.22 13:13, Kefeng Wang wrote:
On 2022/12/13 19:40, David Hildenbrand wrote:
On 13.12.22 10:27, Kefeng Wang wrote:
Introduce a wrapper function pfn_to_online_folio(), which calls
pfn_to_online_page() and returns the folio of the page found,
or null if no page.
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
include/linux/memory_hotplug.h | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/include/linux/memory_hotplug.h
b/include/linux/memory_hotplug.h
index 9fcbf5706595..e841e4fb52a7 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -265,6 +265,13 @@ static inline void pgdat_kswapd_unlock(pg_data_t
*pgdat) {}
static inline void pgdat_kswapd_lock_init(pg_data_t *pgdat) {}
#endif /* ! CONFIG_MEMORY_HOTPLUG */
+static inline struct folio *pfn_to_online_folio(unsigned long pfn)
+{
+ struct page *page = pfn_to_online_page(pfn);
+
+ return page ? page_folio(page) : NULL;
+}
Who guarantees that page_folio() is safe and stable at that point?
IIRC, that's very tricky. We could have the page concurrently getting
freed and the folio dissolved.
So the caller should consider this, lock or get the folio in the caller?
I think the helper pfn_to_online_folio() as is might be wrong approach.
The caller should convert to a folio after taking precautions that it is
actually safe to do that (e.g., succeeded grabbing a reference first).
--
Thanks,
David / dhildenb
