Re: Kernel falls apart under light memory pressure (i.e. linking vmlinux)

[Andrew Lutomirski <luto@mit.edu>]

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On Sun, May 22, 2011 at 7:12 PM, Minchan Kim <minchan.kim@gmail.com> wrote:
> Could you test below patch based on vanilla 2.6.38.6?
> The expect result is that system hang never should happen.
> I hope this is last test about hang.
>
> Thanks.
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 292582c..1663d24 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -231,8 +231,11 @@ unsigned long shrink_slab(struct shrink_control *shrink,
>       if (scanned == 0)
>               scanned = SWAP_CLUSTER_MAX;
>
> -       if (!down_read_trylock(&shrinker_rwsem))
> -               return 1;       /* Assume we'll be able to shrink next time */
> +       if (!down_read_trylock(&shrinker_rwsem)) {
> +               /* Assume we'll be able to shrink next time */
> +               ret = 1;
> +               goto out;
> +       }
>
>       list_for_each_entry(shrinker, &shrinker_list, list) {
>               unsigned long long delta;
> @@ -286,6 +289,8 @@ unsigned long shrink_slab(struct shrink_control *shrink,
>               shrinker->nr += total_scan;
>       }
>       up_read(&shrinker_rwsem);
> +out:
> +       cond_resched();
>       return ret;
>  }
>
> @@ -2331,7 +2336,7 @@ static bool sleeping_prematurely(pg_data_t
> *pgdat, int order, long remaining,
>        * must be balanced
>        */
>       if (order)
> -               return pgdat_balanced(pgdat, balanced, classzone_idx);
> +               return !pgdat_balanced(pgdat, balanced, classzone_idx);
>       else
>               return !all_zones_ok;
>  }

So far with this patch I can't reproduce the hang or the bogus OOM.

To be completely clear, I have COMPACTION, MIGRATION, and THP off, I'm
running 2.6.38.6, and I have exactly two patches applied.  One is the
attached patch and the other is a the fpu.ko/aesni_intel.ko merger
which I need to get dracut to boot my box.

For fun, I also upgraded to 8GB of RAM and it still works.

--Andy

>
> --
> Kind regards,
> Minchan Kim
>

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commit 1f3111be1f9222636b1d56a8ff5c383ec4fb206b
Author: Andy Lutomirski <luto@mit.edu>
Date:   Mon May 23 12:20:17 2011 -0400

    [Minchan] patch for testing 23-05-2011

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0665520..c9c9c93 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -230,8 +230,11 @@ unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
 	if (scanned == 0)
 		scanned = SWAP_CLUSTER_MAX;
 
-	if (!down_read_trylock(&shrinker_rwsem))
-		return 1;	/* Assume we'll be able to shrink next time */
+	if (!down_read_trylock(&shrinker_rwsem)) {
+		/* Assume we'll be able to shrink next time */
+		ret = 1;
+		goto out;
+	}
 
 	list_for_each_entry(shrinker, &shrinker_list, list) {
 		unsigned long long delta;
@@ -282,6 +285,9 @@ unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
 		shrinker->nr += total_scan;
 	}
 	up_read(&shrinker_rwsem);
+
+out:
+	cond_resched();
 	return ret;
 }
 
@@ -2286,7 +2292,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
 	 * must be balanced
 	 */
 	if (order)
-		return pgdat_balanced(pgdat, balanced, classzone_idx);
+		return !pgdat_balanced(pgdat, balanced, classzone_idx);
 	else
 		return !all_zones_ok;
 }