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

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Date:	Mon, 16 May 2011 07:58:01 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Andrew Lutomirski <luto@....edu>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Mel Gorman <mel@....ul.ie>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: Kernel falls apart under light memory pressure (i.e. linking vmlinux)

On Mon, May 16, 2011 at 12:59 AM, Andrew Lutomirski <luto@....edu> wrote:
> I have no clue, but this patch (from Minchan, whitespace-damaged) seems to help:
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f6b435c..4d24828 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2251,6 +2251,10 @@ static bool sleeping_prematurely(pg_data_t
> *pgdat, int order, long remaining,
>       unsigned long balanced = 0;
>       bool all_zones_ok = true;
>
> +       /* If kswapd has been running too long, just sleep */
> +       if (need_resched())
> +               return false;
> +
>       /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
>       if (remaining)
>               return true;
> @@ -2286,7 +2290,7 @@ 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;
>  }
>
> I haven't tested it very thoroughly, but it's survived much longer
> than an unpatched kernel probably would have under moderate use.
>
> I have no idea what the patch does :)

The reason I sent this is that I think your problem is similar to
recent Jame's one.
https://lkml.org/lkml/2011/4/27/361

What the patch does is [1] fix of "wrong pgdat_balanced return value"
bug and [2] fix of "infinite kswapd bug of non-preemption kernel" on
high-order page.

About [1], kswapd have to sleep if zone balancing is completed but in
1741c877[mm: kswapd: keep kswapd awake for high-order allocations
until a percentage of the node is balanced], we made a mistake that
returns wrong return.
Then, although we complete zone balancing, kswapd doesn't sleep and
calls balance_pgdat. In this case, balance_pgdat rerurns without any
work and kswapd could repeat this work infinitely.


>
> I'm happy to run any tests.  I'm also planning to upgrade from 2GB to
> 8GB RAM soon, which might change something.
>
> --Andy
>



-- 
Kind regards,
Minchan Kim
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