[JFFS2] force the jffs2 GC daemon to behave a bit better (efab0b5d) · Commits · 戴 / test

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>

fs/jffs2/background.c

+11 −7

Original line number	Diff line number	Diff line
		@@ -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.
		*/

Admin message