linux-kernel - Re: [PATCH v2] virtio_balloon: disable oom killer when fill balloon

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Date:	Tue, 26 Apr 2011 18:28:01 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Dave Young <hidave.darkstar@...il.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	kosaki.motohiro@...fujitsu.com, linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH v2] virtio_balloon: disable oom killer when fill balloon

Please resend this with [2/2] to linux-mm.

On Tue, Apr 26, 2011 at 5:59 PM, Dave Young <hidave.darkstar@...il.com> wrote:
> When memory pressure is high, virtio ballooning will probably cause oom killing.
> Even if alloc_page with GFP_NORETRY itself does not directly trigger oom it
> will make memory becoming low then memory alloc of other processes will trigger
> oom killing. It is not desired behaviour.

I can't understand why it is undesirable.
Why do we have to handle it specially?


>
> Here disable oom killer in fill_balloon to address this issue.
> Add code comment as KOSAKI Motohiro's suggestion.
>
> Signed-off-by: Dave Young <hidave.darkstar@...il.com>
> ---
>  drivers/virtio/virtio_balloon.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
>
> --- linux-2.6.orig/drivers/virtio/virtio_balloon.c      2011-04-26 11:39:14.053118406 +0800
> +++ linux-2.6/drivers/virtio/virtio_balloon.c   2011-04-26 16:54:56.419741542 +0800
> @@ -25,6 +25,7 @@
>  #include <linux/freezer.h>
>  #include <linux/delay.h>
>  #include <linux/slab.h>
> +#include <linux/oom.h>
>
>  struct virtio_balloon
>  {
> @@ -102,6 +103,12 @@ static void fill_balloon(struct virtio_b
>        /* We can only do one array worth at a time. */
>        num = min(num, ARRAY_SIZE(vb->pfns));
>
> +       /* Disable oom killer for indirect oom due to our memory consuming
> +        * Currently only hibernation code use oom_killer_disable,

Hmm, Please look at current mmotm. Now oom_killer_disabled is used by
do_try_to_free_pages in mmotm so it could make unnecessary oom kill.

BTW, I can't understand why we need to handle virtio by special.
Could you explain it in detail? :)



-- 
Kind regards,
Minchan Kim
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