bug#29846: scroll and fontify takes longer time for file in slow network

bug#29846: scroll and fontify takes longer time for file in slow network

[Shuguang Sun]

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Hi,

Windows 7, GNU Emacs 27.0.50 (build 1, x86_64-w64-mingw32) of 2017-12-09.

Issue:
I have remote dirver (//server/path) mapped to my windows system (samba?).
The network is slow, and it takes some time to open the file. However,
after I have the file opened and scroll down, it takes a long time to
scroll to the next screen. It gets worse if the jit-lock-debug-mode is on.
After that if I try to scroll back to those has been fontified, it get
fluent as expected.

If I open the same file in a local driver (speed is higher than the network
definitely), the scroll is very fluent.

If I open a txt file (fundmental-mode, not fontification) in the same
remote directory, the scroll actions are fluent as well.

Per my understanding, all actions should be done in memory when a file has
been read into buffer, except backup, autosave, etc. The response should
not depents on where the file located phically.

How to repeat it:
1. Find a slow transfer rate network (sorry, it may be hard)
2. Prepare a long c file, 3-4 screens.
3. take font-lock-mode on (jit-font-mode)
4. Open the c file and scroll down, scroll down, scroll down...
5. scroll up, scroll up, scroll up

I have tried profiler. It indicates, the jit-font and redisplay take
majority of the cpu time.
1. open the c file
2. profiler-start
3. scroll down, scroll down, scroll down...
4. profiler-report


Best Regards,
Shuguang Sun

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bug#29846: scroll and fontify takes longer time for file in slow network

[Shuguang Sun]

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Backup, auto-save, and lockfiles has been disabled in .dir-locals

((nil
  (make-backup-files . nil)
  (create-lockfiles  . nil)
  (auto-save-default . nil)
  (auto-save-timeout . 10000)
  ))

Best Regards,
Shuguang

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bug#29846: scroll and fontify takes longer time for file in slow network

[Eli Zaretskii]

On December 25, 2017 11:47:52 AM GMT+02:00, Shuguang Sun <shuguang@gmail.com> wrote:
> Backup, auto-save, and lockfiles has been disabled in .dir-locals
> 
> ((nil
>   (make-backup-files . nil)
>   (create-lockfiles  . nil)
>   (auto-save-default . nil)
>   (auto-save-timeout . 10000)
>   ))
> 
> Best Regards,
> Shuguang

Did you try setting auto-save-interval to a large value, in addition to above?

bug#29846: scroll and fontify takes longer time for file in slow network

[Shuguang Sun]

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>
> Did you try setting auto-save-interval to a large value, in addition to
> above?
>

No difference.
Otherwise, it will not get smoothly to scroll back to those has been viewed
/ fontified.

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bug#29846: scroll and fontify takes longer time for file in slow network

[Eli Zaretskii]

> From: Shuguang Sun <shuguang@gmail.com>
> Date: Mon, 25 Dec 2017 17:47:52 +0800
> 
> Backup, auto-save, and lockfiles has been disabled in .dir-locals
> 
> ((nil
>   (make-backup-files . nil)
>   (create-lockfiles  . nil)
>   (auto-save-default . nil)
>   (auto-save-timeout . 10000)
>   ))

You've disabled file locking, but Emacs still checks whether some
other Emacs session locked the file.  It does that as part of
restore-buffer-modified-p, which is called by JIT font-lock (because
fontification makes the buffer modified and JIT font-lock needs to
undo that after it fontifies a chunk of buffer).  Checking whether a
file is locked entails calling unlock_file, which in turn calls
read_lock_data, which tries to open the lock file.  I'm guessing that
this is slow on that remote volume of yours.

Maybe we should support a special value of create-lockfiles which
would mean don't create lockfiles and don't test fro lockfiles created
by other Emacs sessions.

bug#29846: scroll and fontify takes longer time for file in slow network

[Shuguang Sun]

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On Tue, Dec 26, 2017 at 12:48 AM, Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Shuguang Sun <shuguang@gmail.com>
> > Date: Mon, 25 Dec 2017 17:47:52 +0800
> >
> > Backup, auto-save, and lockfiles has been disabled in .dir-locals
> >
> > ((nil
> >   (make-backup-files . nil)
> >   (create-lockfiles  . nil)
> >   (auto-save-default . nil)
> >   (auto-save-timeout . 10000)
> >   ))
>
> You've disabled file locking, but Emacs still checks whether some
> other Emacs session locked the file.  It does that as part of
> restore-buffer-modified-p, which is called by JIT font-lock (because
> fontification makes the buffer modified and JIT font-lock needs to
> undo that after it fontifies a chunk of buffer).  Checking whether a
> file is locked entails calling unlock_file, which in turn calls
> read_lock_data, which tries to open the lock file.  I'm guessing that
> this is slow on that remote volume of yours.
>
> Maybe we should support a special value of create-lockfiles which
> would mean don't create lockfiles and don't test fro lockfiles created
> by other Emacs sessions.
>

It makes sense. It has a short delayed reponse when I start to modify the
buffer (input, delete, etc.).
It will help single user if we can have a special value of create-lockfiles.

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bug#29846: scroll and fontify takes longer time for file in slow network

[Stefan Monnier]

> I have remote drive (//server/path) mapped to my windows system (samba?).
> The network is slow, and it takes some time to open the file. However,
> after I have the file opened and scroll down, it takes a long time to
> scroll to the next screen. It gets worse if the jit-lock-debug-mode is on.
> After that if I try to scroll back to those has been fontified, it get
> fluent as expected.

I believe this bug was introduced by yours truly
in commit 6bc76cee212aab0a2c02f8c28213fc842cc7880f:

  Author: Stefan Monnier <monnier@iro.umontreal.ca>
  Date:   Tue Apr 8 21:48:07 2014 -0400

    * src/insdel.c (prepare_to_modify_buffer_1): Cancel lock-file checks and
    region handling (and don't call signal_before_change) if
    inhibit_modification_hooks is set.
    (signal_before_change): Don't check inhibit_modification_hooks any more.
    * lisp/subr.el (with-silent-modifications): Don't bind deactivate-mark,
    buffer-file-name, and buffer-file-truename any more.

And I think the patch below hence belongs in emacs-26.  Any objection?


        Stefan


diff --git a/src/buffer.c b/src/buffer.c
index 75cb470af8..f518e72f9e 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -1346,7 +1346,6 @@ It is not ensured that mode lines will be updated to show the modified
 state of the current buffer.  Use with care.  */)
   (Lisp_Object flag)
 {
-  Lisp_Object fn;
 
   /* If buffer becoming modified, lock the file.
      If buffer becoming unmodified, unlock the file.  */
@@ -1355,15 +1354,18 @@ state of the current buffer.  Use with care.  */)
     ? current_buffer->base_buffer
     : current_buffer;
 
-  fn = BVAR (b, file_truename);
-  /* Test buffer-file-name so that binding it to nil is effective.  */
-  if (!NILP (fn) && ! NILP (BVAR (b, filename)))
+  if (!inhibit_modification_hooks)
     {
-      bool already = SAVE_MODIFF < MODIFF;
-      if (!already && !NILP (flag))
-	lock_file (fn);
-      else if (already && NILP (flag))
-	unlock_file (fn);
+      Lisp_Object fn = BVAR (b, file_truename);
+      /* Test buffer-file-name so that binding it to nil is effective.  */
+      if (!NILP (fn) && ! NILP (BVAR (b, filename)))
+        {
+          bool already = SAVE_MODIFF < MODIFF;
+          if (!already && !NILP (flag))
+	    lock_file (fn);
+          else if (already && NILP (flag))
+	    unlock_file (fn);
+        }
     }
 
   /* Here we have a problem.  SAVE_MODIFF is used here to encode

bug#29846: scroll and fontify takes longer time for file in slow network

[Eli Zaretskii]

> From: Stefan Monnier <monnier@IRO.UMontreal.CA>
> Date: Wed, 27 Dec 2017 15:49:56 -0500
> Cc: 29846@debbugs.gnu.org
> 
> > I have remote drive (//server/path) mapped to my windows system (samba?).
> > The network is slow, and it takes some time to open the file. However,
> > after I have the file opened and scroll down, it takes a long time to
> > scroll to the next screen. It gets worse if the jit-lock-debug-mode is on.
> > After that if I try to scroll back to those has been fontified, it get
> > fluent as expected.
> 
> I believe this bug was introduced by yours truly
> in commit 6bc76cee212aab0a2c02f8c28213fc842cc7880f:
> 
>   Author: Stefan Monnier <monnier@iro.umontreal.ca>
>   Date:   Tue Apr 8 21:48:07 2014 -0400
> 
>     * src/insdel.c (prepare_to_modify_buffer_1): Cancel lock-file checks and
>     region handling (and don't call signal_before_change) if
>     inhibit_modification_hooks is set.
>     (signal_before_change): Don't check inhibit_modification_hooks any more.
>     * lisp/subr.el (with-silent-modifications): Don't bind deactivate-mark,
>     buffer-file-name, and buffer-file-truename any more.
> 
> And I think the patch below hence belongs in emacs-26.  Any objection?

LGTM, please push to emacs-26.

Thanks.

bug#29846: scroll and fontify takes longer time for file in slow network

[Stefan Monnier]

>> I believe this bug was introduced by yours truly
>> in commit 6bc76cee212aab0a2c02f8c28213fc842cc7880f:
[...]
>> And I think the patch below hence belongs in emacs-26.  Any objection?
> LGTM, please push to emacs-26.

Installed,


        Stefan