# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1621091402 -7200
# Node ID ab84389f975e9a0d1132f1ee404d4cd133bbda2d
# Parent  d3ed5dc0b98dcf5e123a55a20a22b9fc2496cef5
Make page flushing depend on whether flexpages experience write accesses.

diff -r d3ed5dc0b98d -r ab84389f975e libfsserver/lib/mapping/page_mapper.cc
--- a/libfsserver/lib/mapping/page_mapper.cc	Fri May 07 00:31:02 2021 +0200
+++ b/libfsserver/lib/mapping/page_mapper.cc	Sat May 15 17:10:02 2021 +0200
@@ -184,7 +184,9 @@
 {
     if (flexpage->decrement() || purge)
     {
-        _accessor->flush(flexpage);
+        if (flexpage->modified())
+            _accessor->flush(flexpage);
+
         ipc_unmap_flexpage(flexpage);
         flexpage->invalidate();
     }
diff -r d3ed5dc0b98d -r ab84389f975e libmem/include/mem/flexpage.h
--- a/libmem/include/mem/flexpage.h	Fri May 07 00:31:02 2021 +0200
+++ b/libmem/include/mem/flexpage.h	Sat May 15 17:10:02 2021 +0200
@@ -67,6 +67,8 @@
 
     void upgrade(flags_t flags);
 
+    bool modified();
+
     SendFlexpage to_send(offset_t offset, offset_t hot_spot, flags_t flags,
                          offset_t max_offset=0);
 
diff -r d3ed5dc0b98d -r ab84389f975e libmem/lib/src/flexpage.cc
--- a/libmem/lib/src/flexpage.cc	Fri May 07 00:31:02 2021 +0200
+++ b/libmem/lib/src/flexpage.cc	Sat May 15 17:10:02 2021 +0200
@@ -19,6 +19,8 @@
  * Boston, MA  02110-1301, USA
  */
 
+#include <l4/re/c/dataspace.h>
+
 #include <algorithm>
 
 #include "flexpage.h"
@@ -113,6 +115,14 @@
         _flags |= flags;
 }
 
+/* Return whether the flexpage has been modified due to write access having been
+   granted for any user of the page. */
+
+bool Flexpage::modified()
+{
+    return _flags & L4RE_DS_MAP_FLAG_RW;
+}
+
 /* Return a "send" flexpage for an access to 'offset' by positioning it relative
    to 'hot_spot' for the receive flexpage window. */