linux-kernel - Re: [PATCH] kvm: add oom notifier for virtio balloon

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Message-ID: <AANLkTinoOkZ50B8SUvU=bZLiopSFpamGm+abHaC9CWLX@mail.gmail.com>
Date:	Sat, 9 Oct 2010 11:19:12 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, avi@...hat.com,
	Rusty Russell <rusty@...tcorp.com.au>,
	Anthony Liguori <anthony@...emonkey.ws>
Subject: Re: [PATCH] kvm: add oom notifier for virtio balloon

On Fri, Oct 8, 2010 at 11:53 PM, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> * Dave Young <hidave.darkstar@...il.com> [2010-10-08 21:33:02]:
>
>> On Fri, Oct 8, 2010 at 9:09 PM, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
>> > * Dave Young <hidave.darkstar@...il.com> [2010-10-05 20:45:21]:
>> >
>> >> Balloon could cause guest memory oom killing and panic.
>> >>
>> >> Add oom notify to leak some memory and retry fill balloon after 5 minutes.
>> >>
>> >> At the same time add a mutex to protect balloon operations
>> >> because we need leak balloon in oom notifier and give back freed value.
>> >>
>> >> Thanks Anthony Liguori for his sugestion about inflate retrying.
>> >> Sometimes it will cause endless inflate/oom/delay loop,
>> >> so I think next step is to add an option to do noretry-when-oom balloon.
>> >>
>> >> Signed-off-by: Dave Young <hidave.darkstar@...il.com>
>> >
>> > Won't __GFP_NORETRY prevent OOM? Could you please describe how you
>> > tested the patch?
>>
>> I have not tried __GFP_NORETRY, it should work, but balloon thread
>> will keep wasting cpu resource to allocating.
>>
>>
>> To test the patch, just balloon to small than minimal memory.
>>
>> I use "balloon 30" in qemu monitor to limit slackware guest memory
>> usage. The normal memory used is ~40M.
>>
>> Actually we need to differentiate the process which caused oom. If it
>> is balloon thread we should just stop ballooning, if it is others we
>> can do something like this patch, e.g. retry ballooning after 5
>> minutes.
>
> Ideally the balloon thread should never OOM with __GFP_NORETRY (IIRC).
> The other situation should be dealt with, we should free up any pages
> we have. I wonder if the timeout should be a sysctl tunable.

balbir, you are right,  the oom is not from balloon alloc_page.
balloon thread cause memory low, then afterwards vm readahead code
cause oom. With oom notifier patch oom killing does not happen in my
test

>
> --
>        Three Cheers,
>        Balbir
>



-- 
Regards
dave
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