Index: share/man/man9/Makefile
===================================================================
--- share/man/man9/Makefile
+++ share/man/man9/Makefile
@@ -401,6 +401,7 @@
 	vn_isdisk.9 \
 	vnet.9 \
 	vnode.9 \
+	vnode_pager_purge_range.9 \
 	VOP_ACCESS.9 \
 	VOP_ACLCHECK.9 \
 	VOP_ADVISE.9 \
Index: share/man/man9/vnode_pager_purge_range.9
===================================================================
--- /dev/null
+++ share/man/man9/vnode_pager_purge_range.9
@@ -0,0 +1,73 @@
+.\"
+.\" SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+.\"
+.\" Copyright (c) 2021 The FreeBSD Foundation
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.Dd January 26, 2021
+.Dt VNODE_PAGER_PURGE_RANGE 9
+.Os
+.Sh NAME
+.Nm vnode_pager_purge_range
+.Nd "invalidate the content of the given range in bytes from cache"
+.Sh SYNOPSIS
+.In vm/vm_extern.h
+.Ft void
+.Fn vnode_pager_purge_range "struct vnode *vp" "vm_ooffset_t startoff" "vm_ooffset_t endoff"
+.Sh DESCRIPTION
+.Nm
+invalidates content of the cache covered by the given range from the
+specified vnode
+.Fa vp .
+The range to be purged is
+.Eo [
+.Fa startoff , endoff
+.Ec ) .
+Affected pages within the specified range will be tossed away.
+.Sh IMPLEMENTATION NOTES
+Within the specified range,
+in case
+.Fa startoff
+or
+.Fa endoff
+is not aligned to page boundaries,
+partial-page area will be zeroed.
+In partial-page area,
+for content occupying whole blocks within block
+boundaries,
+the dirty bits for the corresponding blocks will be cleared.
+.Sh LOCKING
+Writer lock of the VM object of
+.Fa vp
+will be held within the function.
+.Sh SEE ALSO
+.Xr vnode 9
+.Sh HISTORY
+The
+.Nm
+manual page first appeared in
+.Fx 14 .
+.Sh AUTHORS
+This
+manual page was written by
+.An Ka Ho Ng Aq Mt khng@freebsdfoundation.org .
Index: sys/vm/vm_extern.h
===================================================================
--- sys/vm/vm_extern.h
+++ sys/vm/vm_extern.h
@@ -120,6 +120,7 @@
 void vmspace_exitfree(struct proc *);
 void vmspace_switch_aio(struct vmspace *);
 void vnode_pager_setsize(struct vnode *, vm_ooffset_t);
+void vnode_pager_purge_range(struct vnode *, vm_ooffset_t, vm_ooffset_t);
 int vslock(void *, size_t);
 void vsunlock(void *, size_t);
 struct sf_buf *vm_imgact_map_page(vm_object_t object, vm_ooffset_t offset);
Index: sys/vm/vnode_pager.c
===================================================================
--- sys/vm/vnode_pager.c
+++ sys/vm/vnode_pager.c
@@ -421,6 +421,49 @@
 	return TRUE;
 }
 
+/*
+ * Internal routine clearing partial-page content
+ */
+static void
+vnode_pager_subpage_purge(struct vm_page *m, int base, int end)
+{
+	int size = end - base;
+
+	/*
+	 * Clear out partial-page garbage in case
+	 * the page has been mapped.
+	 */
+	pmap_zero_page_area(m, base, size);
+
+	/*
+	 * Update the valid bits to reflect the blocks
+	 * that have been zeroed.  Some of these valid
+	 * bits may have already been set.
+	 */
+	vm_page_set_valid_range(m, base, size);
+
+	/*
+	 * Round up "base" to the next block boundary so
+	 * that the dirty bit for a partially zeroed
+	 * block is not cleared.
+	 */
+	base = roundup2(base, DEV_BSIZE);
+	end = rounddown2(end, DEV_BSIZE);
+
+	if (end > base) {
+		/*
+		 * Clear out partial-page dirty bits.
+		 *
+		 * note that we do not clear out the
+		 * valid bits.  This would prevent
+		 * bogus_page replacement from working
+		 * properly.
+		 */
+		vm_page_clear_dirty(m, base, end - base);
+	}
+
+}
+
 /*
  * Lets the VM system know about a change in size for a file.
  * We adjust our own internal size and flush any cached pages in
@@ -483,39 +526,9 @@
 		m = vm_page_grab(object, OFF_TO_IDX(nsize), VM_ALLOC_NOCREAT);
 		if (m == NULL)
 			goto out;
-		if (!vm_page_none_valid(m)) {
-			int base = (int)nsize & PAGE_MASK;
-			int size = PAGE_SIZE - base;
-
-			/*
-			 * Clear out partial-page garbage in case
-			 * the page has been mapped.
-			 */
-			pmap_zero_page_area(m, base, size);
-
-			/*
-			 * Update the valid bits to reflect the blocks that
-			 * have been zeroed.  Some of these valid bits may
-			 * have already been set.
-			 */
-			vm_page_set_valid_range(m, base, size);
-
-			/*
-			 * Round "base" to the next block boundary so that the
-			 * dirty bit for a partially zeroed block is not
-			 * cleared.
-			 */
-			base = roundup2(base, DEV_BSIZE);
-
-			/*
-			 * Clear out partial-page dirty bits.
-			 *
-			 * note that we do not clear out the valid
-			 * bits.  This would prevent bogus_page
-			 * replacement from working properly.
-			 */
-			vm_page_clear_dirty(m, base, PAGE_SIZE - base);
-		}
+		if (!vm_page_none_valid(m))
+			vnode_pager_subpage_purge(m, (int)nsize & PAGE_MASK,
+			    PAGE_SIZE);
 		vm_page_xunbusy(m);
 	}
 out:
@@ -528,6 +541,66 @@
 	VM_OBJECT_WUNLOCK(object);
 }
 
+/*
+ * Lets the VM system know about the purged range for a file. We toss away any
+ * cached pages in the associated object that are affected by the purge
+ * operation. Partial-page area not aligned to page boundaries will be zeroed
+ * and the dirty blocks in DEV_BSIZE unit within a page will not be flushed.
+ *
+ * Write lock of the VM object in vnode will be held.
+ */
+void
+vnode_pager_purge_range(
+    struct vnode *vp, vm_ooffset_t startoff, vm_ooffset_t endoff)
+{
+	struct vm_page *m;
+	struct vm_object *object;
+	vm_pindex_t pgrmidx;
+	bool same_page;
+
+	object = vp->v_object;
+	pgrmidx = OFF_TO_IDX(startoff + PAGE_MASK);
+	same_page = OFF_TO_IDX(startoff) == OFF_TO_IDX(endoff);
+	if (object == NULL || endoff <= startoff)
+		return;
+
+	VM_OBJECT_WLOCK(object);
+
+	if (pgrmidx < OFF_TO_IDX(endoff))
+		vm_object_page_remove(object, pgrmidx,
+		    OFF_TO_IDX(endoff), 0);
+
+	if ((startoff & PAGE_MASK) != 0) {
+		int base = (int)startoff & PAGE_MASK;
+		int end = same_page ? (int)endoff & PAGE_MASK : PAGE_SIZE;
+
+		m = vm_page_grab(vp->v_object, OFF_TO_IDX(startoff),
+		    VM_ALLOC_NOCREAT);
+		if (m != NULL) {
+			if (!vm_page_none_valid(m))
+				vnode_pager_subpage_purge(m, base, end);
+			vm_page_xunbusy(m);
+		}
+
+		if (same_page)
+			goto out;
+	}
+	if ((endoff & PAGE_MASK) != 0) {
+		int base = same_page ? (int)startoff & PAGE_MASK : 0 ;
+		int end = (int)endoff & PAGE_MASK;
+
+		m = vm_page_grab(vp->v_object, OFF_TO_IDX(endoff),
+		    VM_ALLOC_NOCREAT);
+		if (m != NULL) {
+			if (!vm_page_none_valid(m))
+				vnode_pager_subpage_purge(m, base, end);
+			vm_page_xunbusy(m);
+		}
+	}
+out:
+	VM_OBJECT_WUNLOCK(object);
+}
+
 /*
  * calculate the linear (byte) disk address of specified virtual
  * file address