linux-kernel - Re: Found the commit that causes the OOMs

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Date:	Sun, 28 Jun 2009 00:52:20 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	David Howells <dhowells@...hat.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	"riel@...hat.com" <riel@...hat.com>,
	"minchan.kim@...il.com" <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"tytso@....edu" <tytso@....edu>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"elladan@...imo.com" <elladan@...imo.com>,
	"npiggin@...e.de" <npiggin@...e.de>
Subject: Re: Found the commit that causes the OOMs

> Here is the patch in question:
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7592d8e..879d034 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1570,7 +1570,7 @@ static void shrink_zone(int priority, struct zone *zone,
>         * Even if we did not try to evict anon pages at all, we want to
>         * rebalance the anon lru active/inactive ratio.
>         */
> -       if (inactive_anon_is_low(zone, sc))
> +       if (inactive_anon_is_low(zone, sc) && nr_swap_pages > 0)
>                shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);
>
>        throttle_vm_writeout(sc->gfp_mask);
>
> When this was discussed, I think we missed that nr_swap_pages can
> actually get zero on swap systems as well and this should have been
> total_swap_pages - otherwise we also stop balancing the two anon lists
> when swap is _full_ which was not the intention of this change at all.
>
> [ There is another one hiding in shrink_zone() that does the same - it
> was moved from get_scan_ratio() and is pretty old but we still kept
> the inactive/active ratio halfway sane without MinChan's patch. ]
>
> This is from your OOM-run dmesg, David:
>
>  Adding 32k swap on swapfile22.  Priority:-21 extents:1 across:32k
>  Adding 32k swap on swapfile23.  Priority:-22 extents:1 across:32k
>  Adding 32k swap on swapfile24.  Priority:-23 extents:3 across:44k
>  Adding 32k swap on swapfile25.  Priority:-24 extents:1 across:32k
>
> So we actually have swap?  Or are those removed again before the OOM?

[grep to ltp source file]

ltp/testcases/kernel/syscalls/swapon/swapon03.c makes a lot of swap,
but it was removed when the test exit.

Then, When OOM happed, David's system don't have any swap. I don't think
your patch strike the target, unfortunately.
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