From: Martin Pieuchot <mpi@grenadille.net>
Subject: Stop accessing uvmexp.free in uvmpd_scan_inactive()
To: tech@openbsd.org
Date: Tue, 5 Nov 2024 11:52:02 +0100

We compute a `shortage' amount earlier in the loop.  Pass this amount to
uvmpd_scan_inactive() and use it to decide when it freed enough pages.

ok?

Index: uvm/uvm_pdaemon.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_pdaemon.c,v
diff -u -p -r1.119 uvm_pdaemon.c
--- uvm/uvm_pdaemon.c	3 Nov 2024 08:02:15 -0000	1.119
+++ uvm/uvm_pdaemon.c	5 Nov 2024 09:34:09 -0000
@@ -104,7 +104,7 @@ extern unsigned long drmbackoff(long);
  struct rwlock	*uvmpd_trylockowner(struct vm_page *);
  void		uvmpd_scan(struct uvm_pmalloc *, int, int,
  		    struct uvm_constraint_range *);
-int		uvmpd_scan_inactive(struct uvm_pmalloc *,
+int		uvmpd_scan_inactive(struct uvm_pmalloc *, int,
  		    struct uvm_constraint_range *);
  void		uvmpd_tune(void);
  void		uvmpd_drop(struct pglist *);
@@ -422,11 +422,11 @@ uvmpd_dropswap(struct vm_page *pg)
   * => we return TRUE if we are exiting because we met our target
   */
  int
-uvmpd_scan_inactive(struct uvm_pmalloc *pma,
+uvmpd_scan_inactive(struct uvm_pmalloc *pma, int shortage,
      struct uvm_constraint_range *constraint)
  {
  	struct pglist *pglst = &uvm.page_inactive;
-	int free, result, freed = 0;
+	int result, freed = 0;
  	struct vm_page *p, *nextpg;
  	struct uvm_object *uobj;
  	struct vm_page *pps[SWCLUSTPAGES], **ppsp;
@@ -470,9 +470,8 @@ uvmpd_scan_inactive(struct uvm_pmalloc *
  			/*
  			 * see if we've met our target
  			 */
-			free = uvmexp.free - BUFPAGES_DEFICIT;
  			if (((pma == NULL || (pma->pm_flags & UVM_PMA_FREED)) &&
-			    (free + uvmexp.paging >= uvmexp.freetarg)) ||
+			    (uvmexp.paging >= (shortage - freed))) ||
  			    dirtyreacts == UVMPD_NUMDIRTYREACTS) {
  				if (swslot == 0) {
  					/* exit now if no swap-i/o pending */
@@ -569,7 +568,7 @@ uvmpd_scan_inactive(struct uvm_pmalloc *
  			 * free target when all the current pageouts complete.
  			 */
  			if ((pma == NULL || (pma->pm_flags & UVM_PMA_FREED)) &&
-			    (free + uvmexp.paging > uvmexp.freetarg)) {
+			    (uvmexp.paging > (shortage - freed))) {
  				rw_exit(slock);
  				continue;
  			}
@@ -893,7 +892,7 @@ uvmpd_scan(struct uvm_pmalloc *pma, int  	 * we work 
on meeting our inactive target by converting active pages
  	 * to inactive ones.
  	 */
-	pages_freed = uvmpd_scan_inactive(pma, constraint);
+	pages_freed = uvmpd_scan_inactive(pma, shortage, constraint);
  	uvmexp.pdfreed += pages_freed;
  	shortage -= pages_freed;