Introduce a function to trylock a page instead of duplicating the logic.

Stolen from NetBSD.

ok jsg@

diff --git a/sys/uvm/uvm_pdaemon.c b/sys/uvm/uvm_pdaemon.c
index 2b07728..350f95e 100644 (file)
--- a/sys/uvm/uvm_pdaemon.c
+++ b/sys/uvm/uvm_pdaemon.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: uvm_pdaemon.c,v 1.103 2022/08/30 08:30:58 mpi Exp $   */
+/*     $OpenBSD: uvm_pdaemon.c,v 1.104 2022/08/31 09:26:04 mpi Exp $   */
 /*     $NetBSD: uvm_pdaemon.c,v 1.23 2000/08/20 10:24:14 bjh21 Exp $   */
 
 /*
@@ -101,6 +101,7 @@ extern void drmbackoff(long);
  * local prototypes
  */
 
+struct rwlock  *uvmpd_trylockowner(struct vm_page *);
 void           uvmpd_scan(struct uvm_pmalloc *);
 void           uvmpd_scan_inactive(struct uvm_pmalloc *, struct pglist *);
 void           uvmpd_tune(void);
@@ -367,6 +368,34 @@ uvm_aiodone_daemon(void *arg)
        }
 }
 
+/*
+ * uvmpd_trylockowner: trylock the page's owner.
+ *
+ * => return the locked rwlock on success.  otherwise, return NULL.
+ */
+struct rwlock *
+uvmpd_trylockowner(struct vm_page *pg)
+{
+
+       struct uvm_object *uobj = pg->uobject;
+       struct rwlock *slock;
+
+       if (uobj != NULL) {
+               slock = uobj->vmobjlock;
+       } else {
+               struct vm_anon *anon = pg->uanon;
+
+               KASSERT(anon != NULL);
+               slock = anon->an_lock;
+       }
+
+       if (rw_enter(slock, RW_WRITE|RW_NOSLEEP)) {
+               return NULL;
+       }
+
+       return slock;
+}
+
 
 /*
  * uvmpd_dropswap: free any swap allocated to this page.
@@ -474,51 +503,43 @@ uvmpd_scan_inactive(struct uvm_pmalloc *pma, struct pglist *pglst)
 
                        anon = p->uanon;
                        uobj = p->uobject;
-                       if (p->pg_flags & PQ_ANON) {
+
+                       /*
+                        * first we attempt to lock the object that this page
+                        * belongs to.  if our attempt fails we skip on to
+                        * the next page (no harm done).  it is important to
+                        * "try" locking the object as we are locking in the
+                        * wrong order (pageq -> object) and we don't want to
+                        * deadlock.
+                        */
+                       slock = uvmpd_trylockowner(p);
+                       if (slock == NULL) {
+                               continue;
+                       }
+
+                       /*
+                        * move referenced pages back to active queue
+                        * and skip to next page.
+                        */
+                       if (pmap_is_referenced(p)) {
+                               uvm_pageactivate(p);
+                               rw_exit(slock);
+                               uvmexp.pdreact++;
+                               continue;
+                       }
+
+                       if (p->pg_flags & PG_BUSY) {
+                               rw_exit(slock);
+                               uvmexp.pdbusy++;
+                               continue;
+                       }
+
+                       /* does the page belong to an object? */
+                       if (uobj != NULL) {
+                               uvmexp.pdobscan++;
+                       } else {
                                KASSERT(anon != NULL);
-                               slock = anon->an_lock;
-                               if (rw_enter(slock, RW_WRITE|RW_NOSLEEP)) {
-                                       /* lock failed, skip this page */
-                                       continue;
-                               }
-                               /*
-                                * move referenced pages back to active queue
-                                * and skip to next page.
-                                */
-                               if (pmap_is_referenced(p)) {
-                                       uvm_pageactivate(p);
-                                       rw_exit(slock);
-                                       uvmexp.pdreact++;
-                                       continue;
-                               }
-                               if (p->pg_flags & PG_BUSY) {
-                                       rw_exit(slock);
-                                       uvmexp.pdbusy++;
-                                       continue;
-                               }
                                uvmexp.pdanscan++;
-                       } else {
-                               KASSERT(uobj != NULL);
-                               slock = uobj->vmobjlock;
-                               if (rw_enter(slock, RW_WRITE|RW_NOSLEEP)) {
-                                       continue;
-                               }
-                               /*
-                                * move referenced pages back to active queue
-                                * and skip to next page.
-                                */
-                               if (pmap_is_referenced(p)) {
-                                       uvm_pageactivate(p);
-                                       rw_exit(slock);
-                                       uvmexp.pdreact++;
-                                       continue;
-                               }
-                               if (p->pg_flags & PG_BUSY) {
-                                       rw_exit(slock);
-                                       uvmexp.pdbusy++;
-                                       continue;
-                               }
-                               uvmexp.pdobscan++;
                        }
 
                        /*
@@ -858,14 +879,11 @@ uvmpd_scan(struct uvm_pmalloc *pma)
 {
        int free, inactive_shortage, swap_shortage, pages_freed;
        struct vm_page *p, *nextpg;
-       struct uvm_object *uobj;
-       struct vm_anon *anon;
        struct rwlock *slock;
 
        MUTEX_ASSERT_LOCKED(&uvm.pageqlock);
 
        uvmexp.pdrevs++;                /* counter */
-       uobj = NULL;
 
        /*
         * get current "free" page count
@@ -926,19 +944,9 @@ uvmpd_scan(struct uvm_pmalloc *pma)
                /*
                 * lock the page's owner.
                 */
-               if (p->uobject != NULL) {
-                       uobj = p->uobject;
-                       slock = uobj->vmobjlock;
-                       if (rw_enter(slock, RW_WRITE|RW_NOSLEEP)) {
-                               continue;
-                       }
-               } else {
-                       anon = p->uanon;
-                       KASSERT(p->uanon != NULL);
-                       slock = anon->an_lock;
-                       if (rw_enter(slock, RW_WRITE|RW_NOSLEEP)) {
-                               continue;
-                       }
+               slock = uvmpd_trylockowner(p);
+               if (slock == NULL) {
+                       continue;
                }
 
                /*