Re: Software suspend testing in 2.6.0-test1

[Andrew Morton <akpm@osdl.org>]

Pavel Machek <pavel@ucw.cz> wrote:
>
> > --- linux/mm/vmscan.c.old	Thu Jul 17 21:30:09 2003
> > +++ linux/mm/vmscan.c	Thu Jul 17 21:29:58 2003
> > @@ -930,7 +930,7 @@
> >  		}
> >  		if (all_zones_ok)
> >  			break;
> > -		blk_congestion_wait(WRITE, HZ/10);
> > +		blk_congestion_wait(WRITE, HZ/50);
> >  	}
> >  	return nr_pages - to_free;
> >  }
> 
> This is certainly not okay. Andrew, you know more about vm
> internals... What does this ugly constant mean?

Most of the time the timeout is a "can't happen" - blk_congestion_wait() is
terminated by completion of writeout.  The timeout is mainly there to
prevent hangs if weird and rare races happen.  Otherwise we'd need lots
more locking.

I don't think we want to be calling it at all if reclaim is working well. 
Something like this.


diff -puN mm/vmscan.c~a mm/vmscan.c
--- 25/mm/vmscan.c~a	Thu Jul 17 13:05:36 2003
+++ 25-akpm/mm/vmscan.c	Thu Jul 17 13:05:58 2003
@@ -921,7 +921,7 @@ static int balance_pgdat(pg_data_t *pgda
 			if (i < ZONE_HIGHMEM) {
 				reclaim_state->reclaimed_slab = 0;
 				shrink_slab(max_scan + nr_mapped, GFP_KERNEL);
-				to_free += reclaim_state->reclaimed_slab;
+				to_free -= reclaim_state->reclaimed_slab;
 			}
 			if (zone->all_unreclaimable)
 				continue;
@@ -930,7 +930,8 @@ static int balance_pgdat(pg_data_t *pgda
 		}
 		if (all_zones_ok)
 			break;
-		blk_congestion_wait(WRITE, HZ/10);
+		if (to_free)
+			blk_congestion_wait(WRITE, HZ/10);
 	}
 	return nr_pages - to_free;
 }

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