linux-kernel - Re: [PATCH v2 4/6] mm: introduce common page state for ballooned memory

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Date:	Mon, 22 Sep 2014 22:40:34 +0400
From:	Konstantin Khlebnikov <koct9i@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Konstantin Khlebnikov <k.khlebnikov@...sung.com>,
	Rafael Aquini <aquini@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: [PATCH v2 4/6] mm: introduce common page state for ballooned memory

On Sat, Sep 20, 2014 at 10:23 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Sat, 20 Sep 2014 09:25:01 +0400 Konstantin Khlebnikov <koct9i@...il.com> wrote:
>
>> >
>> > So I'm going to send "fix for
>> > mm-balloon_compaction-use-common-page-ballooning-v2" to Linus
>> > separately, but it has no changelog at all.
>>
>> Probably it would be better if you drop everything except actually
>> fixes and stresstest. This is gone too far, now balloon won't compile
>> in the middle of patchset. Just tell me and I'll redo the rest.
>
> I think it's best if I drop everything:
>
> mm-balloon_compaction-ignore-anonymous-pages.patch
> mm-balloon_compaction-keep-ballooned-pages-away-from-normal-migration-path.patch
> mm-balloon_compaction-isolate-balloon-pages-without-lru_lock.patch
> selftests-vm-transhuge-stress-stress-test-for-memory-compaction.patch
> mm-introduce-common-page-state-for-ballooned-memory.patch
> mm-balloon_compaction-use-common-page-ballooning.patch
> mm-balloon_compaction-general-cleanup.patch
> mm-balloon_compaction-use-common-page-ballooning-v2-fix-1.patch
>
> Please go through it and send out a new version?
>
>

I've found yet another bug in this code. It seems here is a nest.
balloon_page_dequeue can race with  balloon_page_isolate:
balloon_page_isolate can remove page from list between
llist_for_each_entry_safe and trylock_page in balloon_page_dequeue.
balloon_page_dequeue runs under mutex_lock(&vb->balloon_lock);
both of them lock page using trylock_page so race is tight but it is
not impossible.
Probably it's really easier to rewrite it than to fix bugs one by one =/
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