linux-kernel - Re: [PATCH v2 05/11] md/raid5: add scribble region for buffer lists

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Message-id: <20090608172535.GA28448@clouds>
Date:	Mon, 08 Jun 2009 13:25:35 -0400
From:	Jody McIntyre <scjody@....com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Neil Brown <neilb@...e.de>, linux-raid@...r.kernel.org,
	maan@...temlinux.org, linux-kernel@...r.kernel.org,
	yur@...raft.com, hpa@...or.com
Subject: Re: [PATCH v2 05/11] md/raid5: add scribble region for buffer lists

On Fri, Jun 05, 2009 at 12:19:07PM -0700, Dan Williams wrote:
> One of the design goals was to prevent the occurrence of the
> softlockup watchdog events which seem to trigger on large raid6
> resyncs.  A per-cpu scheme would still require preempt_disable() while
> the calculation is active, so perhaps we just need a call to
> cond_resched() in raid5d to appease the scheduler.

FWIW we added this to the patches shipped with Lustre:

Index: linux-2.6.18-128.1.1/drivers/md/raid5.c
===================================================================
--- linux-2.6.18-128.1.1.orig/drivers/md/raid5.c
+++ linux-2.6.18-128.1.1/drivers/md/raid5.c
@@ -2987,6 +2987,8 @@ static void raid5d (mddev_t *mddev)
 		handle_stripe(sh, conf->spare_page);
 		release_stripe(sh);
 
+		cond_resched();
+
 		spin_lock_irq(&conf->device_lock);
 	}
 	PRINTK("%d stripes handled\n", handled);

I thought most of these issues were gone in more recent kernels, but we
haven't tested RAID on anything other than RHEL 4+5 extensively (Lustre
doesn't support sufficiently new kernels yet.)

Cheers,
Jody
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