[Trac #1292] JFFS file system pathological use.

[Zarro Boogs per Child]

#1292: JFFS file system pathological use.
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 Reporter:  jg       |       Owner:  dwmw2  
     Type:  defect   |      Status:  new    
 Priority:  blocker  |   Milestone:  BTest-4
Component:  kernel   |    Keywords:  jffs2  
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 Writing log files (or similar files) one short piece at a time
 (unbuffered) and then flushing them to stable storage is bad for the
 flash, as it causes many unnecessary writes to the flash; much better
 would be to defer such writing until some amount of time has passed, and
 then flush, so that multiple small writes can be merged into a single
 write.  Do not build applications with such behavior.

 Michailis, as part of his mesh networking work, had such log files, that
 ran for days, and generated many megabyte long log files that were written
 one line at a time.  This exposed a JFFS2 file system bug such that at
 boot time, particularly on systems of 128 meg of RAM, would fill memory
 with log messages while JFFS2 attempted to mount the file system (filling
 memory with nodes for all these tiny writes), causing the system to oops
 at boot time.  This bug appeared after years of use of JFFS2 due to the
 increasing size of flash with this particularly pathological behavior.

 This is related to ticket #248; while not identical, we've moved common
 directories where most log files are written off of flash, and that will
 be marked a duplicate of this bug.

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Ticket URL: <http://dev.laptop.org/ticket/1292>
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