From: mpi <mpi@openbsd.org>
Date: Fri, 27 Oct 2023 19:18:53 +0000 (+0000)
Subject: Make out-of-swap checks more robust.
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=cb3ee63add04c3a8de3c9e9efbbe3a498ee80f1d;p=openbsd

Make out-of-swap checks more robust.

Consider that the swap space is full when 99% of it is filled with pages that
are no longer present in memory.  This prevents deadlocks when out-of-swap if
some swap ranges had I/O errors and have been marked as 'bad', or if some
pages are unreachable by the pagedaemon and still holding some slots.

Also introduce uvm_swapisfilled() to check if there are some free slots in
the swap.  Note that we consider the swap space completly filled if it is not
possible to write a full cluster.  This prevents deadlocks if a few slots are
never allocated.

ok miod@
---

diff --git a/sys/uvm/uvm_pdaemon.c b/sys/uvm/uvm_pdaemon.c
index 445102eed80..1b99b190c92 100644
--- a/sys/uvm/uvm_pdaemon.c
+++ b/sys/uvm/uvm_pdaemon.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uvm_pdaemon.c,v 1.108 2023/10/24 10:00:22 mpi Exp $	*/
+/*	$OpenBSD: uvm_pdaemon.c,v 1.109 2023/10/27 19:18:53 mpi Exp $	*/
 /*	$NetBSD: uvm_pdaemon.c,v 1.23 2000/08/20 10:24:14 bjh21 Exp $	*/
 
 /*
@@ -595,11 +595,8 @@ uvmpd_scan_inactive(struct uvm_pmalloc *pma,
 			 * is full, free any swap allocated to the page
 			 * so that other pages can be paged out.
 			 */
-			KASSERT(uvmexp.swpginuse <= uvmexp.swpages);
-			if ((p->pg_flags & PQ_SWAPBACKED) &&
-			    uvmexp.swpginuse == uvmexp.swpages) {
+			if ((p->pg_flags & PQ_SWAPBACKED) && uvm_swapisfilled())
 				uvmpd_dropswap(p);
-			}
 
 			/*
 			 * the page we are looking at is dirty.   we must
@@ -917,9 +914,7 @@ uvmpd_scan(struct uvm_pmalloc *pma, struct uvm_constraint_range *constraint)
 	 */
 	free = uvmexp.free - BUFPAGES_DEFICIT;
 	swap_shortage = 0;
-	if (free < uvmexp.freetarg &&
-	    uvmexp.swpginuse == uvmexp.swpages &&
-	    !uvm_swapisfull() &&
+	if (free < uvmexp.freetarg && uvm_swapisfilled() && !uvm_swapisfull() &&
 	    pages_freed == 0) {
 		swap_shortage = uvmexp.freetarg - free;
 	}
diff --git a/sys/uvm/uvm_swap.c b/sys/uvm/uvm_swap.c
index 27963259eba..1818cc06384 100644
--- a/sys/uvm/uvm_swap.c
+++ b/sys/uvm/uvm_swap.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uvm_swap.c,v 1.166 2023/01/10 11:18:47 kettenis Exp $	*/
+/*	$OpenBSD: uvm_swap.c,v 1.167 2023/10/27 19:18:53 mpi Exp $	*/
 /*	$NetBSD: uvm_swap.c,v 1.40 2000/11/17 11:39:39 mrg Exp $	*/
 
 /*
@@ -1516,8 +1516,30 @@ ReTry:	/* XXXMRG */
 }
 
 /*
- * uvm_swapisfull: return true if all of available swap is allocated
- * and in use.
+ * uvm_swapisfilled: return true if the amount of free space in swap is
+ * smaller than the size of a cluster.
+ *
+ * As long as some swap slots are being used by pages currently in memory,
+ * it is possible to reuse them.  Even if the swap space has been completly
+ * filled we do not consider it full.
+ */
+int
+uvm_swapisfilled(void)
+{
+	int result;
+
+	mtx_enter(&uvm_swap_data_lock);
+	KASSERT(uvmexp.swpginuse <= uvmexp.swpages);
+	result = (uvmexp.swpginuse + SWCLUSTPAGES) >= uvmexp.swpages;
+	mtx_leave(&uvm_swap_data_lock);
+
+	return result;
+}
+
+/*
+ * uvm_swapisfull: return true if the amount of pages only in swap
+ * accounts for more than 99% of the total swap space.
+ *
  */
 int
 uvm_swapisfull(void)
@@ -1526,7 +1548,7 @@ uvm_swapisfull(void)
 
 	mtx_enter(&uvm_swap_data_lock);
 	KASSERT(uvmexp.swpgonly <= uvmexp.swpages);
-	result = (uvmexp.swpgonly == uvmexp.swpages);
+	result = (uvmexp.swpgonly >= (uvmexp.swpages * 99 / 100));
 	mtx_leave(&uvm_swap_data_lock);
 
 	return result;
diff --git a/sys/uvm/uvm_swap.h b/sys/uvm/uvm_swap.h
index 9904fe58cd7..58b0bfc9a61 100644
--- a/sys/uvm/uvm_swap.h
+++ b/sys/uvm/uvm_swap.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uvm_swap.h,v 1.19 2022/06/28 19:19:34 mpi Exp $	*/
+/*	$OpenBSD: uvm_swap.h,v 1.20 2023/10/27 19:18:53 mpi Exp $	*/
 /*	$NetBSD: uvm_swap.h,v 1.5 2000/01/11 06:57:51 chs Exp $	*/
 
 /*
@@ -42,6 +42,7 @@ int			uvm_swap_put(int, struct vm_page **, int, int);
 int			uvm_swap_alloc(int *, boolean_t);
 void			uvm_swap_free(int, int);
 void			uvm_swap_markbad(int, int);
+int			uvm_swapisfilled(void);
 int			uvm_swapisfull(void);
 void			uvm_swap_freepages(struct vm_page **, int);
 #ifdef HIBERNATE
diff --git a/sys/uvm/uvmexp.h b/sys/uvm/uvmexp.h
index de5f5fa367c..7d0225786fd 100644
--- a/sys/uvm/uvmexp.h
+++ b/sys/uvm/uvmexp.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uvmexp.h,v 1.10 2022/08/29 11:09:31 mpi Exp $	*/
+/*	$OpenBSD: uvmexp.h,v 1.11 2023/10/27 19:18:53 mpi Exp $	*/
 
 #ifndef	_UVM_UVMEXP_
 #define	_UVM_UVMEXP_
@@ -83,7 +83,7 @@ struct uvmexp {
 	/* swap */
 	int nswapdev;	/* [S] number of configured swap devices in system */
 	int swpages;	/* [S] number of PAGE_SIZE'ed swap pages */
-	int swpginuse;	/* [K] number of swap pages in use */
+	int swpginuse;	/* [S] number of swap pages in use */
 	int swpgonly;	/* [a] number of swap pages in use, not also in RAM */
 	int nswget;	/* [a] number of swap pages moved from disk to RAM */
 	int nanon;	/* XXX number total of anon's in system */