[src/trunk]: src/sys/fs/tmpfs tmpfs_write(): use UBC_FAULTBUSY when extending...

[ad <ad%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/f3e9619d2e3c
branches:  trunk
changeset: 972367:f3e9619d2e3c
user:      ad <ad%NetBSD.org@localhost>
date:      Sun May 24 20:08:26 2020 +0000

description:
tmpfs_write(): use UBC_FAULTBUSY when extending files, if possible, to avoid
zeroing of newly allocated pages & fault processing.

diffstat:

 sys/fs/tmpfs/tmpfs_vnops.c |  28 ++++++++++++++++++++++++----
 1 files changed, 24 insertions(+), 4 deletions(-)

diffs (63 lines):

diff -r c89e5eb253fd -r f3e9619d2e3c sys/fs/tmpfs/tmpfs_vnops.c
--- a/sys/fs/tmpfs/tmpfs_vnops.c        Sun May 24 20:05:53 2020 +0000
+++ b/sys/fs/tmpfs/tmpfs_vnops.c        Sun May 24 20:08:26 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: tmpfs_vnops.c,v 1.141 2020/05/19 22:22:15 ad Exp $     */
+/*     $NetBSD: tmpfs_vnops.c,v 1.142 2020/05/24 20:08:26 ad Exp $     */
 
 /*
  * Copyright (c) 2005, 2006, 2007, 2020 The NetBSD Foundation, Inc.
@@ -35,7 +35,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: tmpfs_vnops.c,v 1.141 2020/05/19 22:22:15 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: tmpfs_vnops.c,v 1.142 2020/05/24 20:08:26 ad Exp $");
 
 #include <sys/param.h>
 #include <sys/dirent.h>
@@ -573,7 +573,7 @@
        tmpfs_node_t *node;
        struct uvm_object *uobj;
        off_t oldsize;
-       int error;
+       int error, ubc_flags;
 
        KASSERT(VOP_ISLOCKED(vp));
 
@@ -603,6 +603,26 @@
                        goto out;
        }
 
+       /*
+        * If we're extending the file and have data to write that would
+        * not leave an un-zeroed hole, we can avoid fault processing and
+        * zeroing of pages on allocation.
+        *
+        * Don't do this if the file is mapped and we need to touch an
+        * existing page, because writing a mapping of the file into itself
+        * could cause a deadlock on PG_BUSY.
+        *
+        * New pages will not become visible until finished here (because
+        * of PG_BUSY and the vnode lock).
+        */
+       ubc_flags = UBC_WRITE | UBC_VNODE_FLAGS(vp);
+       if (uio->uio_offset >= oldsize &&
+           ((uio->uio_offset & (PAGE_SIZE - 1)) == 0 ||
+           ((vp->v_vflag & VV_MAPPED) == 0 &&
+           trunc_page(uio->uio_offset) == trunc_page(oldsize)))) {
+               ubc_flags |= UBC_FAULTBUSY;
+       }
+
        uobj = node->tn_spec.tn_reg.tn_aobj;
        error = 0;
        while (error == 0 && uio->uio_resid > 0) {
@@ -613,7 +633,7 @@
                        break;
                }
                error = ubc_uiomove(uobj, uio, len, IO_ADV_DECODE(ioflag),
-                   UBC_WRITE | UBC_VNODE_FLAGS(vp));
+                   ubc_flags);
        }
        if (error) {
                (void)tmpfs_reg_resize(vp, oldsize);