[Trac #65] Temporary filesystems should be in RAM

[Zarro Boogs per Child]

#65: Temporary filesystems should be in RAM
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 Reporter:  wmb at firmworks.com  |        Owner:  jg      
     Type:  defect             |       Status:  assigned
 Priority:  blocker            |    Milestone:  BTest-1 
Component:  kernel             |   Resolution:          
 Keywords:                     |  
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Changes (by jg):

  * owner:  marcelo => jg
  * priority:  high => blocker
  * status:  new => assigned

Comment:

 Start with a jffs2 image from build 131.  Mount it under OFW, scanning
 the summary and loading abbreviated versions of all the summary nodes
 into memory.  The data  summary nodes take up about 1.4 MiB (87K  data
 summary nodes at 16 bytes per).  (JFFS2 calls them inodes, but that name
 gives the wrong idea if you think of conventional Unix inodes).

 Now leave Linux running for a couple of hours or so, with the mouse
 unplugged so X keeps bouncing up and down.

 Shut down the system cleanly, reboot, and mount it under OFW again.

 Now the data summary nodes take up 8 MB.  Yes, Virginia, the data
 summary area has grown by a factor of 5.7 *while the system is basically
 not being used*.

 Where is it all coming from?

 For starters, there are 2547 junk entries in /tmp, mostly of the form:

   .X0-lock
   .tX0-lock
   sh-thd-1149890225   (lots of different values for this number)

 But that doesn't explain the data node explosion, because those /tmp
 things are mostly directory entry nodes.

 Another hotspot is /var/log, which contains 768 entries, nearly all
 copies of
   Xorg.0.log
   Xorg.0.log.old

 That is the directory nodes. Let's look at the data nodes for a typical
 copy of Xorg.0.log.  Here's one with inum=5ce2.  Oh look, there are 1036
 separate data nodes for that log file.  I'll bet it makes a separate
 node for every line that is appended.  ... Yep, that's what is in the
 nodes, one line per node.  And there are over 200 superseded copies of
 that file in /var/log

 If we poke around in the summary node array we see that the last 6+ MiB
 is mostly just copies of /var/log/Xorg.0.log .

-- 
Ticket URL: <http://dev.laptop.org/ticket/65#comment:11>
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