From: Andrea Arcangeli <aarcange@redhat.com>
To: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
linux-mm@kvack.org, Andi Kleen <andi@firstfloor.org>,
Wu Fengguang <fengguang.wu@intel.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH 2/3] pagemap: export KPF_THP
Date: Mon, 19 Dec 2011 22:23:48 +0100 [thread overview]
Message-ID: <20111219212348.GP16411@redhat.com> (raw)
In-Reply-To: <4EEFA51D.2050707@linux.vnet.ibm.com>
On Mon, Dec 19, 2011 at 12:57:01PM -0800, Dave Hansen wrote:
> But, every single one of the pagemap flags is really just a snapshot
> KPF_DIRTY, KPF_LOCKED, etc... The entire interface is inherently a racy
> snapshot, and there's not a whole lot you can do about it.
Having read the discussion, while I don't see a big need of the
KPF_THP, I also see how it in certain corner cases it can be used to
test memory failure injection and I agree with you on the above. Maybe
it can also be used to check if at certain virtual offsets
(pid/pagemap lookup followed by a kpageflags lookup) we always fail to
find THP inside big vmas, maybe out of not aligned mprotect that may
be optimized by aligning it.
The other kernel internal bits may also be stale and go away quicker
than the KPF_THP, so I don't see a problem in exposing it. We also
provide THP related info in meminfo/smaps, if they were supposed to be
invisible that wouldn't be allowed too.
A bigger concern to me is that the new bitfield alters the protocol,
but old code by adding one more bit (if sanely coded...) shouldn't break.
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next prev parent reply other threads:[~2011-12-19 21:24 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-19 18:38 [RFC][PATCH 0/3] pagemap handles transparent hugepage Naoya Horiguchi
2011-12-19 18:38 ` [RFC][PATCH 1/3] pagemap: avoid splitting thp when reading /proc/pid/pagemap Naoya Horiguchi
2011-12-19 18:45 ` Andi Kleen
2011-12-19 18:48 ` David Rientjes
2011-12-19 19:16 ` Naoya Horiguchi
2011-12-19 18:38 ` [RFC][PATCH 2/3] pagemap: export KPF_THP Naoya Horiguchi
2011-12-19 18:40 ` Andi Kleen
2011-12-19 18:49 ` David Rientjes
2011-12-19 18:55 ` Naoya Horiguchi
2011-12-19 19:05 ` Andrea Arcangeli
2011-12-19 19:24 ` KOSAKI Motohiro
2011-12-19 20:26 ` Naoya Horiguchi
2011-12-19 20:48 ` KOSAKI Motohiro
2011-12-19 21:20 ` Naoya Horiguchi
2011-12-19 20:31 ` Dave Hansen
2011-12-19 20:45 ` KOSAKI Motohiro
2011-12-19 20:57 ` Dave Hansen
2011-12-19 21:23 ` Andrea Arcangeli [this message]
2011-12-20 3:35 ` Wu Fengguang
2011-12-20 18:10 ` Naoya Horiguchi
2011-12-19 18:38 ` [RFC][PATCH 3/3] pagemap: document KPF_THP and show make page-types aware of it Naoya Horiguchi
2011-12-19 18:51 ` David Rientjes
2011-12-20 3:41 ` Wu Fengguang
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