On Fri, Oct 09, 2020 at 02:34:34PM -0700, Eric Biggers wrote:

On Fri, Oct 09, 2020 at 12:49:57PM -0700, ira.weiny@intel.com wrote:

quoted

The kmap() calls in this FS are localized to a single thread.  To avoid
the over head of global PKRS updates use the new kmap_thread() call.

@@ -2410,12 +2410,12 @@ static inline struct page *f2fs_pagecache_get_page(
 
 static inline void f2fs_copy_page(struct page *src, struct page *dst)
 {
-	char *src_kaddr = kmap(src);
-	char *dst_kaddr = kmap(dst);
+	char *src_kaddr = kmap_thread(src);
+	char *dst_kaddr = kmap_thread(dst);
 
 	memcpy(dst_kaddr, src_kaddr, PAGE_SIZE);
-	kunmap(dst);
-	kunmap(src);
+	kunmap_thread(dst);
+	kunmap_thread(src);
 }

Wouldn't it make more sense to switch cases like this to kmap_atomic()?
The pages are only mapped to do a memcpy(), then they're immediately unmapped.

Maybe you missed the earlier thread from Thomas trying to do something
similar for rather different reasons ...

https://lore.kernel.org/lkml/20200919091751.011116649@linutronix.de/ (local)