linux-kernel - Re: kernel 3.0: BUG: soft lockup: find_get

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Date:	Wed, 19 Oct 2011 12:42:15 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Mel Gorman <mgorman@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Pawel Sikora <pluto@...k.net>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	jpiszcz@...idpixels.com, arekm@...-linux.org,
	linux-kernel@...r.kernel.org
Subject: Re: kernel 3.0: BUG: soft lockup: find_get_pages+0x51/0x110

On Wed, 19 Oct 2011, Linus Torvalds wrote:
> On Wed, Oct 19, 2011 at 12:43 AM, Mel Gorman <mgorman@...e.de> wrote:
> >
> > My vote is with the migration change. While there are occasionally
> > patches to make migration go faster, I don't consider it a hot path.
> > mremap may be used intensively by JVMs so I'd loathe to hurt it.
> 
> Ok, everybody seems to like that more, and it removes code rather than
> adds it, so I certainly prefer it too. Pawel, can you test that other
> patch (to mm/migrate.c) that Hugh posted? Instead of the mremap vma
> locking patch that you already verified for your setup?
> 
> Hugh - that one didn't have a changelog/sign-off, so if you could
> write that up, and Pawel's testing is successful, I can apply it...
> Looks like we have acks from both Andrea and Mel.

Yes, I'm glad to have that input from Andrea and Mel, thank you.

Here we go.  I can't add a Tested-by since Pawel was reporting on the
alternative patch, but perhaps you'll be able to add that in later.

I may have read too much into Pawel's mail, but it sounded like he
would have expected an eponymous find_get_pages() lockup by now,
and was pleased that this patch appeared to have cured that.

I've spent quite a while trying to explain find_get_pages() lockup by
a missed migration entry, but I just don't see it: I don't expect this
(or the alternative) patch to do anything to fix that problem.  I won't
mind if it magically goes away, but I expect we'll need more info from
the debug patch I sent Justin a couple of days ago.

Ah, I'd better send the patch separately as
"[PATCH] mm: fix race between mremap and removing migration entry":
Pawel's "l" makes my old alpine setup choose quoted printable when
I reply to your mail.

Hugh
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