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[JFFS2] force the jffs2 GC daemon to behave a bit better

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I've noticed some pretty poor behavior on OLPC machines after bootup, when
gdm/X are starting.  The GCD monopolizes the scheduler (which in turns
means it gets to do more nand i/o), which results in processes taking much
much longer than they should to start.

As an example, on an OLPC machine going from OFW to a usable X (via
auto-login gdm) takes 2m 30s.  The majority of this time is consumed by
the switch into graphical mode.  With this patch, we cut a full 60s off of
bootup time.  After bootup, things are much snappier as well.

Note that we have seen a CRC node error with this patch that causes the machine
to fail to boot, but we've also seen that problem without this patch.

Signed-off-by: Andres Salomon <dilinger@debian.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
This commit is contained in:
Andres Salomon 2009-02-11 13:27:02 -08:00 committed by David Woodhouse
parent ab00d68276
commit efab0b5d3e
1 changed files with 11 additions and 7 deletions
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18
fs/jffs2/background.c
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@ -95,13 +95,17 @@ static int jffs2_garbage_collect_thread(void *_c)
spin_unlock(&c->erase_completion_lock);
/* This thread is purely an optimisation. But if it runs when
other things could be running, it actually makes things a
lot worse. Use yield() and put it at the back of the runqueue
every time. Especially during boot, pulling an inode in
with read_inode() is much preferable to having the GC thread
get there first. */
yield();
/* Problem - immediately after bootup, the GCD spends a lot
* of time in places like jffs2_kill_fragtree(); so much so
* that userspace processes (like gdm and X) are starved
* despite plenty of cond_resched()s and renicing. Yield()
* doesn't help, either (presumably because userspace and GCD
* are generally competing for a higher latency resource -
* disk).
* This forces the GCD to slow the hell down. Pulling an
* inode in with read_inode() is much preferable to having
* the GC thread get there first. */
schedule_timeout_interruptible(msecs_to_jiffies(50));
/* Put_super will send a SIGKILL and then wait on the sem.
*/