Improve interactive file-saving performance

* src/fileio.c (init_fileio):
No longer any need to set write-region-inhibit-fsync here.
(syms_of_fileio): Default write-region-inhibit-fsync to t (Bug#60474).

1 files changed, 16 insertions, 21 deletions

diff --git a/src/fileio.c b/src/fileio.c
index 7fb7f5ddc5e..c672e0f7baf 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -6334,24 +6334,6 @@ init_fileio (void)
   umask (realmask);
 
   valid_timestamp_file_system = 0;
-
-  /* fsync can be a significant performance hit.  Often it doesn't
-     suffice to make the file-save operation survive a crash.  For
-     batch scripts, which are typically part of larger shell commands
-     that don't fsync other files, its effect on performance can be
-     significant so its utility is particularly questionable.
-     Hence, for now by default fsync is used only when interactive.
-
-     For more on why fsync often fails to work on today's hardware, see:
-     Zheng M et al. Understanding the robustness of SSDs under power fault.
-     11th USENIX Conf. on File and Storage Technologies, 2013 (FAST '13), 271-84
-     https://www.usenix.org/system/files/conference/fast13/fast13-final80.pdf
-
-     For more on why fsync does not suffice even if it works properly, see:
-     Roche X. Necessary step(s) to synchronize filename operations on disk.
-     Austin Group Defect 672, 2013-03-19
-     https://austingroupbugs.net/view.php?id=672  */
-  write_region_inhibit_fsync = noninteractive;
 }
 
 void
@@ -6609,9 +6591,22 @@ file is usually more useful if it contains the deleted text.  */);
   DEFVAR_BOOL ("write-region-inhibit-fsync", write_region_inhibit_fsync,
 	       doc: /* Non-nil means don't call fsync in `write-region'.
 This variable affects calls to `write-region' as well as save commands.
-Setting this to nil may avoid data loss if the system loses power or
-the operating system crashes.  By default, it is non-nil in batch mode.  */);
-  write_region_inhibit_fsync = 0; /* See also `init_fileio' above.  */
+By default, it is non-nil.
+
+Although setting this to nil may avoid data loss if the system loses power,
+it can be a significant performance hit in the usual case, and it doesn't
+necessarily cause file-save operations to actually survive a crash.  */);
+
+  /* For more on why fsync often fails to work on today's hardware, see:
+     Zheng M et al. Understanding the robustness of SSDs under power fault.
+     11th USENIX Conf. on File and Storage Technologies, 2013 (FAST '13), 271-84
+     https://www.usenix.org/system/files/conference/fast13/fast13-final80.pdf
+
+     For more on why fsync does not suffice even if it works properly, see:
+     Roche X. Necessary step(s) to synchronize filename operations on disk.
+     Austin Group Defect 672, 2013-03-19
+     https://austingroupbugs.net/view.php?id=672  */
+  write_region_inhibit_fsync = true;
 
   DEFVAR_BOOL ("delete-by-moving-to-trash", delete_by_moving_to_trash,
                doc: /* Specifies whether to use the system's trash can.