To reduce accesses to the global `uvmexp.free', I'd like know how many
pages have been freed by every "shrinker".  In this case change 
uvm_pmr_cache_drain() such that it returns the number of freed pages.

ok?

Index: uvm/uvm_pmemrange.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_pmemrange.c,v
diff -u -p -r1.67 uvm_pmemrange.c
--- uvm/uvm_pmemrange.c	18 Aug 2024 08:18:49 -0000	1.67
+++ uvm/uvm_pmemrange.c	30 Sep 2024 08:11:15 -0000
@@ -2279,7 +2279,7 @@ uvm_pmr_cache_get(int flags)
 	return pg;
 }
 
-void
+unsigned int
 uvm_pmr_cache_free(struct uvm_pmr_cache_item *upci)
 {
 	struct pglist pgl;
@@ -2296,6 +2296,8 @@ uvm_pmr_cache_free(struct uvm_pmr_cache_
 	atomic_sub_int(&uvmexp.percpucaches, upci->upci_npages);
 	upci->upci_npages = 0;
 	memset(upci->upci_pages, 0, sizeof(upci->upci_pages));
+
+	return i;
 }
 
 void
@@ -2337,16 +2339,19 @@ uvm_pmr_cache_put(struct vm_page *pg)
 	splx(s);
 }
 
-void
+unsigned int
 uvm_pmr_cache_drain(void)
 {
 	struct uvm_pmr_cache *upc = &curcpu()->ci_uvm;
+	unsigned int freed = 0;
 	int s;
 
 	s = splvm();
-	uvm_pmr_cache_free(&upc->upc_magz[0]);
-	uvm_pmr_cache_free(&upc->upc_magz[1]);
+	freed += uvm_pmr_cache_free(&upc->upc_magz[0]);
+	freed += uvm_pmr_cache_free(&upc->upc_magz[1]);
 	splx(s);
+
+	return freed;
 }
 
 #else /* !(MULTIPROCESSOR && __HAVE_UVM_PERCPU) */
@@ -2363,8 +2368,9 @@ uvm_pmr_cache_put(struct vm_page *pg)
 	uvm_pmr_freepages(pg, 1);
 }
 
-void
+unsigned int
 uvm_pmr_cache_drain(void)
 {
+	return 0;
 }
 #endif
Index: uvm/uvm_pmemrange.h
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_pmemrange.h,v
diff -u -p -r1.17 uvm_pmemrange.h
--- uvm/uvm_pmemrange.h	1 May 2024 12:54:27 -0000	1.17
+++ uvm/uvm_pmemrange.h	30 Sep 2024 08:11:15 -0000
@@ -149,7 +149,7 @@ struct vm_page		*uvm_pmr_extract_range(s
 			    struct pglist *);
 struct vm_page		*uvm_pmr_cache_get(int);
 void			 uvm_pmr_cache_put(struct vm_page *);
-void			 uvm_pmr_cache_drain(void);
+unsigned int		 uvm_pmr_cache_drain(void);
 
 
 #endif /* _UVM_UVM_PMEMRANGE_H_ */