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From: Andrea Arcangeli <>
To: Hugh Dickins <>
Cc: KAMEZAWA Hiroyuki <>,
	Daisuke Nishimura <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>
Subject: Re: [mmotm] BUG: Bad page state in process khugepaged ?
Date: Fri, 11 Feb 2011 21:24:31 +0100	[thread overview]
Message-ID: <20110211202431.GJ3347@random.random> (raw)
In-Reply-To: <alpine.LSU.2.00.1102111132560.3814@sister.anvils>

On Fri, Feb 11, 2011 at 11:58:58AM -0800, Hugh Dickins wrote:
> Oh, I hadn't realized Fedora use it.  I wonder if that's wise, I thought
> Nick introduced it partly for the more expensive checks, and there might
> be one or two of those around - those bad_range()s in page_alloc.c?

I doubt the more expensive checks are very measurable.. benchmarks
usually run on enterprise distro. I'm sure when they enabled, they
were aware of having to run more expensive runtime checks.

> But the patch actually says -1024*1024: either would do.

I actually increased it to -1024*1024 after writing the email ;) sorry
the for the confusion.

> Yes, that's fine, 0xfff00000 looks unlikely enough (and my
> imagination for "deadbeef"-like magic is too drowsy today).

I used a negative power of two even if I doubt the compiler can make
much use of it.

> Okay I suppose: it seems rather laboured to me, I think I'd have just
> moved the VM_BUG_ON into rmv_page_order() if I'd done the patch; but
> since I was too lazy to do it, I'd better be grateful for yours!

Ok the reason I didn't move the VM_BUG_ON is to be stricter in case
there are more usages of __ClearPageBuddy in the future. I guess it's
not so important, but when I initially implemented it, it wasn't
entirely obvious it would work safe with memory hotplug, compaction
and all other bits using PageBuddy, so...

  reply	other threads:[~2011-02-11 20:24 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-02-09  6:10 KAMEZAWA Hiroyuki
2011-02-09  6:40 ` KAMEZAWA Hiroyuki
2011-02-09  6:50 ` Daisuke Nishimura
2011-02-09  6:52   ` KAMEZAWA Hiroyuki
2011-02-09 20:07     ` Andrea Arcangeli
2011-02-11  7:02       ` Hugh Dickins
2011-02-11 10:49         ` Andrea Arcangeli
2011-02-11 19:58           ` Hugh Dickins
2011-02-11 20:24             ` Andrea Arcangeli [this message]
2011-02-14 22:24           ` Johannes Weiner
2011-02-09  7:23 ` [PATCH][BUGFIX] memcg: fix leak of accounting at failure path of hugepage collapsing KAMEZAWA Hiroyuki
2011-02-09  7:51   ` Daisuke Nishimura
2011-02-09  9:51   ` Johannes Weiner
2011-02-10  2:49   ` Minchan Kim

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