Re: pdflush and dm-crypt

[Andrew Morton <akpm@osdl.org>]

Jens Axboe <axboe@suse.de> wrote:
>
> On Mon, Mar 29 2004, Zoltan NAGY wrote:
> > Hi!
> > 
> > I've just upgraded the system to 2.6.5-rc2-bk6, and I'm using
> > dm-crypt. It's a heavily used server, on average 20-30mbit/sec
> > traffic is on the wire 7/24, and just noticed, that the load is very
> > high. In every 4-5 sec pdflush takes a lot of cpu... Is this
> > intentional? I've found a similar question on kerneltrap
> > (http://kerneltrap.org/node/view/2756), but havent found a solution
> > yet. I'm just wondering if it is a problem, or it's the normal
> > behavior? It's a 1.8 P4 with 1G ram and highmem enabled, with 256 bit
> > aes thru dm-crypt.
> 
> Try the -mm kernels intead, should have lots better behaviour for
> pdflush/dm interactions.
> 

How come?  Isn't this problem just "gee, we have a lot of stuff to encrypt
during writeback"?  If so, then it should be sufficient to poke a hole in
the encryption loop?

--- 25/drivers/md/dm-crypt.c~a	Mon Mar 29 16:11:49 2004
+++ 25-akpm/drivers/md/dm-crypt.c	Mon Mar 29 16:11:56 2004
@@ -669,6 +669,7 @@ static int crypt_map(struct dm_target *t
 		/* out of memory -> run queues */
 		if (remaining)
 			blk_congestion_wait(bio_data_dir(clone), HZ/100);
+		cond_resched();
 	}
 
 	/* drop reference, clones could have returned before we reach this */

_