From 4dfa06e114ed4332f8ea3b86f9963f475714da1e Mon Sep 17 00:00:00 2001
From: Chuck Silvers <chs@FreeBSD.org>
Date: Fri, 17 Jul 2020 23:09:36 +0000
Subject: [PATCH] Add a new function vm_page_free_invalid() for freeing invalid
 pages that might be wired.  If the page is wired then it cannot be freed now,
 but the thread that eventually unwires it will free it at that point.

Reviewed by:	markj, kib
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D25430
---
 sys/vm/vm_page.c | 25 +++++++++++++++++++++++++
 sys/vm/vm_page.h |  1 +
 2 files changed, 26 insertions(+)

diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index 08420d5da19e..a7d6f3dd9d64 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -1361,6 +1361,31 @@ vm_page_readahead_finish(vm_page_t m)
 	vm_page_xunbusy_unchecked(m);
 }
 
+/*
+ * Destroy the identity of an invalid page and free it if possible.
+ * This is intended to be used when reading a page from backing store fails.
+ */
+void
+vm_page_free_invalid(vm_page_t m)
+{
+
+	KASSERT(vm_page_none_valid(m), ("page %p is valid", m));
+	KASSERT(!pmap_page_is_mapped(m), ("page %p is mapped", m));
+	vm_page_assert_xbusied(m);
+	KASSERT(m->object != NULL, ("page %p has no object", m));
+	VM_OBJECT_ASSERT_WLOCKED(m->object);
+
+	/*
+	 * If someone has wired this page while the object lock
+	 * was not held, then the thread that unwires is responsible
+	 * for freeing the page.  Otherwise just free the page now.
+	 * The wire count of this unmapped page cannot change while
+	 * we have the page xbusy and the page's object wlocked.
+	 */
+	if (vm_page_remove(m))
+		vm_page_free(m);
+}
+
 /*
  *	vm_page_sleep_if_busy:
  *
diff --git a/sys/vm/vm_page.h b/sys/vm/vm_page.h
index 2ed6840bfece..4a073cec8e51 100644
--- a/sys/vm/vm_page.h
+++ b/sys/vm/vm_page.h
@@ -629,6 +629,7 @@ void vm_page_deactivate_noreuse(vm_page_t);
 void vm_page_dequeue(vm_page_t m);
 void vm_page_dequeue_deferred(vm_page_t m);
 vm_page_t vm_page_find_least(vm_object_t, vm_pindex_t);
+void vm_page_free_invalid(vm_page_t);
 vm_page_t vm_page_getfake(vm_paddr_t paddr, vm_memattr_t memattr);
 void vm_page_initfake(vm_page_t m, vm_paddr_t paddr, vm_memattr_t memattr);
 int vm_page_insert (vm_page_t, vm_object_t, vm_pindex_t);