linux-kernel - Re: [PATCH v12 4/7] mm: introduce compaction and migration for ballooned pages

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Date:	Mon, 26 Nov 2012 10:57:54 -0500
From:	Sasha Levin <levinsasha928@...il.com>
To:	Rafael Aquini <aquini@...hat.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Minchan Kim <minchan@...nel.org>,
	Rik van Riel <riel@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH v12 4/7] mm: introduce compaction and migration for
 ballooned pages

On Thu, Nov 22, 2012 at 10:10 AM, Rafael Aquini <aquini@...hat.com> wrote:
> On Thu, Nov 22, 2012 at 09:19:15AM -0500, Sasha Levin wrote:
>> And managed to reproduce it only once through last night, here is the dump I got
>> before the oops:
>>
>> [ 2760.356820] page:ffffea0000d00e00 count:1 mapcount:-2147287036 mapping:00000000000004f4 index:0xd00e00000003
>> [ 2760.362354] page flags: 0x350000000001800(private|private_2)
>>
>
> Thanks alot for following up this one Sasha.
>
>
> We're stumbling across a private page -- seems something in your setup is doing
> this particular usage, and that's probably why I'm not seeing the same here.
>
> Regardless being a particular case or not, we shouldn't be poking at that
> private page, so I figured the tests I'm doing at balloon_page_movable() are
> incomplete and dumb.
>
> Perhaps, a better way to proceed here would be assuring the NR_PAGEFLAGS
> rightmost bits from page->flags are all cleared, as this is the state a page
> coming from buddy to the balloon list will be, and this is the state the balloon
> page flags will be kept as long as it lives as such (we don't play with any flag
> at balloon level).
>
>
> Here goes what I'll propose after you confirm it doesn't trigger your crash
> anymore, as it simplifies the code and reduces the testing battery @
> balloon_page_movable() -- ballooned pages have no flags set, 1 refcount and 0
> mapcount, always.
>
>
> Could you give this a try?
>
> Thank you!

Ran it for a while, no more BUGs, yay :)


Thanks,
Sasha
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