Jffs2 and big file = very slow jffs2_garbage_collect_pass

[Jörn Engel]

On Thu, 17 January 2008 17:12:29 +0100, Matthieu CASTET wrote:
> 
> we have a 240 MB jffs2 partition with summary enabled and no 
> compression. We use 2ad8ee713566671875216ebcec64f2eda47bd19d git jffs2 
> version 
> (http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=2ad8ee713566671875216ebcec64f2eda47bd19d)
> 
> 
> On this partition we have several file (less than 1 MB) and a big file 
> in the root (200 MB).
> 
> The big file is a FAT image that is exported with usb-storage (with usb 
> device) or mounted on a loopback device.
> 
> After some FAT operations, we manage to get in a situation were the 
> jffs2_garbage_collect_pass take 12 minutes.
> 
> jffs2_lookup for the big file (triggered with a ls in the root) take 12 
> minutes.
> 
> If we do a ls without waiting that jffs2_garbage_collect_pass finish, ls 
> takes 12 minutes to complete.

Impressive!  JFFS2 may be slow, but it shouldn't be _that_ slow.  Not
sure who cares enough to look at this.  My approach would be to 
$ echo t > /proc/sysrq_trigger
several times during those 12 minutes and take a close look at the code
paths showing up.  Most likely it will spend 99% of the time in one
place.

Jörn

-- 
...one more straw can't possibly matter...
-- Kirby Bakken