Reducing of JFFS2 mounting time

[Ruslan Satlykov]

Hi all,

Some time ago, we faced a problem with a long mounting of high filled JFFS2 filesystem. 
On 16Mb FLASH partition, the scanning (and mount, respectively) tooks about 4-5 seconds. 
To reduce this time, after looking around of possible ways to improve JFFS2 perfomance in 
this area, we decided to move flash scanning process itself into start of garbage collecting 
thread. While scanning will not be done, no any access from user-space is allowed, of course, 
and we reach it by blocking filesystem with semaphore and counter of already scanned flash blocks. 
Since scanning is executing in different kernel thread, user-space 'mount' released relatively fast. 

After scan completion, block counter will be equal total number of blocks and completion 
semaphore will be released, giving applications right to access filesystem.

In original driver's version, when a filesystem mounted in 'read-only mode', a garbage collection
thread doesn't started; in out modified version, we start this thread anyway, but after scanning 
completes, we check with what flags a mounting has been requested. And if we mounts 'read-only',
thread is terminated as usual.

Attached patch have been tested with MontaVista' MVLCEE 2.4.20 Linux kernel. On 16Mb, 
100% filled JFFS2  flash partition, a mounting tooks about 800ms.

Guys, if anybody have a time, please take a look at attached work. What do you think about it? 
Your opinions?

Thanks, 
Ruslan Satlykov
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