Ensure that pagedaemon wakeups as a result of failed UVM_PLA_NOWAIT

allocations will recover some memory from the dma_constraint range.

The allocation still fails, the intent is to ensure that the
pagedaemon will free some memory to possibly allow a subsequent
allocation to succeed.

This also adds a UVM_PLA_NOWAKE flag to allow special cases in the
buffer cache to not wake up the pagedaemon until they want to.

ok kettenis@

4 files changed, 45 insertions, 11 deletions

diff --git a/sys/kern/vfs_biomem.c b/sys/kern/vfs_biomem.c
index 0f761c976c2..8bdd583fe58 100644
--- a/sys/kern/vfs_biomem.c
+++ b/sys/kern/vfs_biomem.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: vfs_biomem.c,v 1.40 2019/05/08 12:40:57 beck Exp $ */
+/*	$OpenBSD: vfs_biomem.c,v 1.41 2019/05/09 20:36:44 beck Exp $ */
 
 /*
  * Copyright (c) 2007 Artur Grabowski <art@openbsd.org>
@@ -288,7 +288,7 @@ buf_alloc_pages(struct buf *bp, vsize_t size)
 	 */
 	do {
 		i = uvm_pagealloc_multi(buf_object, offs, size,
-		    UVM_PLA_NOWAIT);
+		    UVM_PLA_NOWAIT | UVM_PLA_NOWAKE);
 		if (i == 0)
 			break;
 	} while	(bufbackoff(&dma_constraint, size) == 0);
@@ -359,7 +359,7 @@ buf_realloc_pages(struct buf *bp, struct uvm_constraint_range *where,
 
 	do {
 		r = uvm_pagerealloc_multi(bp->b_pobj, bp->b_poffs,
-		    bp->b_bufsize, UVM_PLA_NOWAIT, where);
+		    bp->b_bufsize, UVM_PLA_NOWAIT | UVM_PLA_NOWAKE, where);
 		if (r == 0)
 			break;
 	} while	((bufbackoff(where, atop(bp->b_bufsize)) == 0));
diff --git a/sys/uvm/uvm_extern.h b/sys/uvm/uvm_extern.h
index 24ddcd98ccd..12dc1f7b32f 100644
--- a/sys/uvm/uvm_extern.h
+++ b/sys/uvm/uvm_extern.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uvm_extern.h,v 1.145 2019/03/01 01:46:18 cheloha Exp $	*/
+/*	$OpenBSD: uvm_extern.h,v 1.146 2019/05/09 20:36:44 beck Exp $	*/
 /*	$NetBSD: uvm_extern.h,v 1.57 2001/03/09 01:02:12 chs Exp $	*/
 
 /*
@@ -151,6 +151,7 @@ typedef int		vm_prot_t;
 #define UVM_PLA_ZERO		0x0004	/* zero all pages before returning */
 #define UVM_PLA_TRYCONTIG	0x0008	/* try to allocate contig physmem */
 #define UVM_PLA_FAILOK		0x0010	/* caller can handle failure */
+#define UVM_PLA_NOWAKE		0x0020	/* don't wake the page daemon on failure */
 
 /*
  * lockflags that control the locking behavior of various functions.
diff --git a/sys/uvm/uvm_pdaemon.c b/sys/uvm/uvm_pdaemon.c
index c0368f66815..1c3c38fd5ea 100644
--- a/sys/uvm/uvm_pdaemon.c
+++ b/sys/uvm/uvm_pdaemon.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uvm_pdaemon.c,v 1.79 2018/01/18 18:08:51 bluhm Exp $	*/
+/*	$OpenBSD: uvm_pdaemon.c,v 1.80 2019/05/09 20:36:44 beck Exp $	*/
 /*	$NetBSD: uvm_pdaemon.c,v 1.23 2000/08/20 10:24:14 bjh21 Exp $	*/
 
 /* 
@@ -186,6 +186,13 @@ uvmpd_tune(void)
 }
 
 /*
+ * Indicate to the page daemon that a nowait call failed and it should
+ * recover at least some memory in the most restricted region (assumed
+ * to be dma_constraint).
+ */
+volatile int uvm_nowait_failed;
+
+/*
  * uvm_pageout: the main loop for the pagedaemon
  */
 void
@@ -205,12 +212,17 @@ uvm_pageout(void *arg)
 	uvm_unlock_pageq();
 
 	for (;;) {
+		int nowaitfailed = 0;
 		long size;
 	  	work_done = 0; /* No work done this iteration. */
 
 		uvm_lock_fpageq();
+		if (uvm_nowait_failed) {
+			nowaitfailed = 1;
+			uvm_nowait_failed = 0;
+		}
 
-		if (TAILQ_EMPTY(&uvm.pmr_control.allocs)) {
+		if (!nowaitfailed && TAILQ_EMPTY(&uvm.pmr_control.allocs)) {
 			msleep(&uvm.pagedaemon, &uvm.fpageqlock, PVM,
 			    "pgdaemon", 0);
 			uvmexp.pdwoke++;
@@ -219,8 +231,16 @@ uvm_pageout(void *arg)
 		if ((pma = TAILQ_FIRST(&uvm.pmr_control.allocs)) != NULL) {
 			pma->pm_flags |= UVM_PMA_BUSY;
 			constraint = pma->pm_constraint;
-		} else
-			constraint = no_constraint;
+		} else {
+			if (nowaitfailed) {
+				/*
+				 * XXX realisticly, this is what our
+				 * nowait callers probably care about
+				 */
+				constraint = dma_constraint;
+			} else
+				constraint = no_constraint;
+		}
 
 		uvm_unlock_fpageq();
 
@@ -243,6 +263,8 @@ uvm_pageout(void *arg)
 		if (uvmexp.free - BUFPAGES_DEFICIT < uvmexp.freetarg)
 			size += uvmexp.freetarg - (uvmexp.free -
 			    BUFPAGES_DEFICIT);
+		if (size == 0)
+			size = 16; /* XXX */
 		uvm_unlock_pageq();
 		(void) bufbackoff(&constraint, size * 2);
 		uvm_lock_pageq();
diff --git a/sys/uvm/uvm_pmemrange.c b/sys/uvm/uvm_pmemrange.c
index dcddfe35a14..cd92c319650 100644
--- a/sys/uvm/uvm_pmemrange.c
+++ b/sys/uvm/uvm_pmemrange.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uvm_pmemrange.c,v 1.53 2016/09/16 02:52:24 dlg Exp $	*/
+/*	$OpenBSD: uvm_pmemrange.c,v 1.54 2019/05/09 20:36:44 beck Exp $	*/
 
 /*
  * Copyright (c) 2009, 2010 Ariane van der Steldt <ariane@stack.nl>
@@ -702,6 +702,13 @@ uvm_pmr_extract_range(struct uvm_pmemrange *pmr, struct vm_page *pg,
 }
 
 /*
+ * Indicate to the page daemon that a nowait call failed and it should
+ * recover at least some memory in the most restricted region (assumed
+ * to be dma_constraint).
+ */
+extern volatile int uvm_nowait_failed;
+
+/*
  * Acquire a number of pages.
  *
  * count:	the number of pages returned
@@ -1014,8 +1021,12 @@ fail:
 		    flags & UVM_PLA_FAILOK) == 0)
 			goto retry;
 		KASSERT(flags & UVM_PLA_FAILOK);
-	} else
-		wakeup(&uvm.pagedaemon);
+	} else {
+		if (!(flags & UVM_PLA_NOWAKE)) {
+			uvm_nowait_failed = 1;
+			wakeup(&uvm.pagedaemon);
+		}
+	}
 	uvm_unlock_fpageq();
 
 	return ENOMEM;