small patch for pageout. Comments?

[Konstantin Belousov]

On Thu, Nov 30, 2017 at 12:30:47PM -0800, Larry McVoy wrote:
> I'll give this patch a try and compare to the pageout patch.

What do you mean by 'compare to ...' ?

BTW, below are some fixes which I found when re-read the changes.
It messed up counters/timeouts.  Better use this.

diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c
index ece496407c2..48b3934ddd5 100644
--- a/sys/vm/vm_fault.c
+++ b/sys/vm/vm_fault.c
@@ -134,6 +134,16 @@ static void vm_fault_dontneed(const struct faultstate *fs, vm_offset_t vaddr,
 static void vm_fault_prefault(const struct faultstate *fs, vm_offset_t addra,
 	    int backward, int forward);
 
+static int vm_pfault_oom_attempts = 3;
+SYSCTL_INT(_vm, OID_AUTO, pfault_oom_attempts, CTLFLAG_RWTUN,
+    &vm_pfault_oom_attempts, 0,
+    "");
+
+static int vm_pfault_oom_wait = 10;
+SYSCTL_INT(_vm, OID_AUTO, pfault_oom_wait, CTLFLAG_RWTUN,
+    &vm_pfault_oom_wait, 0,
+    "");
+
 static inline void
 release_page(struct faultstate *fs)
 {
@@ -531,7 +541,7 @@ vm_fault_hold(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 	vm_pindex_t retry_pindex;
 	vm_prot_t prot, retry_prot;
 	int ahead, alloc_req, behind, cluster_offset, error, era, faultcount;
-	int locked, nera, result, rv;
+	int locked, nera, oom, result, rv;
 	u_char behavior;
 	boolean_t wired;	/* Passed by reference. */
 	bool dead, hardfault, is_first_object_locked;
@@ -543,6 +553,8 @@ vm_fault_hold(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 	hardfault = false;
 
 RetryFault:;
+	oom = 0;
+RetryFault_oom:;
 
 	/*
 	 * Find the backing store object and offset into it to begin the
@@ -787,7 +799,17 @@ RetryFault:;
 			}
 			if (fs.m == NULL) {
 				unlock_and_deallocate(&fs);
-				VM_WAITPFAULT;
+				if (vm_pfault_oom_attempts < 0 ||
+				    oom < vm_pfault_oom_attempts) {
+					oom++;
+					vm_waitpfault(vm_pfault_oom_wait);
+					goto RetryFault_oom;
+				}
+				if (bootverbose)
+					printf(
+	"proc %d (%s) failed to alloc page on fault, starting OOM\n",
+					    curproc->p_pid, curproc->p_comm);
+				vm_pageout_oom(VM_OOM_MEM);
 				goto RetryFault;
 			}
 		}
diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index 4711af9d16d..67c8ddd4b92 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -2724,7 +2724,7 @@ vm_page_alloc_fail(vm_object_t object, int req)
  *	  this balance without careful testing first.
  */
 void
-vm_waitpfault(void)
+vm_waitpfault(int wp)
 {
 
 	mtx_lock(&vm_page_queue_free_mtx);
@@ -2734,7 +2734,7 @@ vm_waitpfault(void)
 	}
 	vm_pages_needed = true;
 	msleep(&vm_cnt.v_free_count, &vm_page_queue_free_mtx, PDROP | PUSER,
-	    "pfault", 0);
+	    "pfault", wp * hz);
 }
 
 struct vm_pagequeue *
diff --git a/sys/vm/vm_pageout.h b/sys/vm/vm_pageout.h
index 2cdb1492fab..bf09d7142d0 100644
--- a/sys/vm/vm_pageout.h
+++ b/sys/vm/vm_pageout.h
@@ -96,11 +96,10 @@ extern bool vm_pages_needed;
  *	Signal pageout-daemon and wait for it.
  */
 
-extern void pagedaemon_wakeup(void);
+void pagedaemon_wakeup(void);
 #define VM_WAIT vm_wait()
-#define VM_WAITPFAULT vm_waitpfault()
-extern void vm_wait(void);
-extern void vm_waitpfault(void);
+void vm_wait(void);
+void vm_waitpfault(int wp);
 
 #ifdef _KERNEL
 int vm_pageout_flush(vm_page_t *, int, int, int, int *, boolean_t *);