bug#9559: 23.2; diff mode refining creates many temporary files causing busy hard disk

bug#9559: 23.2; diff mode refining creates many temporary files causing busy hard disk

[Trevor Spiteri]

When I open a diff file, and one hunk has a lot of changes, I noticed 
that the hard disk becomes busy for quite a bit of time until the 
refinements in the hunk are highlighted. I am including a simple diff 
file a.diff  below which causes the problem to me. The diff file has 40 
changes in one hunk.

I tried to track down what was causing this, and found that the function 
smerge-refine-subst was creating two temporary files and deleting them 
for each part of the hunk, so for the example below it creates and 
deletes 80 temporary files, and the hard disk is a bit busy for about 3 
seconds on my system, just to refine one hunk.

If I modify smerge-refine-subst by changing the lines
          (file1 (make-temp-file "diff1"))
          (file2 (make-temp-file "diff2")))
to
          (file1 "/dev/shm/diff1")
          (file2 "/dev/shm/diff2"))
the hard disk remains quiet and I do not have to wait for 3 seconds, 
presumably because /dev/shm is in RAM, not on the hard disk.

This reminds me of something that nags me a bit, although it is not 
really a problem. Whenever I'm using ediff, moving to the next hunk 
always makes the hard disk work, so I hear a short hard disk sound for 
each hunk I move to. I don't know if this is related.

a.diff:
--- a    2011-09-20 13:08:11.760491820 +0100
+++ b    2011-09-20 13:08:17.891515308 +0100
@@ -2,85 +2,85 @@
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In GNU Emacs 23.2.1 (x86_64-redhat-linux-gnu, GTK+ Version 2.24.4)
  of 2011-05-23 on x86-12.phx2.fedoraproject.org
Windowing system distributor `Fedora Project', version 11.0.11003000
configured using `configure  '--build=x86_64-redhat-linux-gnu' 
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bug#9559: 23.2; diff mode refining creates many temporary files causing busy hard disk

[Stefan Monnier]

> This reminds me of something that nags me a bit, although it is not
> really a problem. Whenever I'm using ediff, moving to the next hunk always
> makes the hard disk work, so I hear a short hard disk sound for each hunk
> I move to. I don't know if this is related.

I'd think the answer for you is to use tmpfs for /tmp rather than only
for /dev/shm.


        Stefan