From: Thomas Gleixner <tglx@linutronix.de>
To: Dave Hansen <dave.hansen@intel.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
Bin Yang <bin.yang@intel.com>, Mark Gross <mark.gross@intel.com>
Subject: Re: [patch V3 09/11] x86/mm/cpa: Optimize same protection check
Date: Thu, 27 Sep 2018 20:07:33 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.21.1809272003160.8118@nanos.tec.linutronix.de> (raw)
In-Reply-To: <9bf16a03-d54f-d424-46fb-d16a80ec5cc5@intel.com>
On Fri, 21 Sep 2018, Dave Hansen wrote:
> On 09/17/2018 07:29 AM, Thomas Gleixner wrote:
> > When the existing mapping is correct and the new requested page protections
> > are the same as the existing ones, then further checks can be omitted and the
> > large page can be preserved. The slow path 4k wise check will not come up with
> > a different result.
> >
> > Before:
> >
> > 1G pages checked: 2
> > 1G pages sameprot: 0
> > 1G pages preserved: 0
> > 2M pages checked: 540
> > 2M pages sameprot: 466
> > 2M pages preserved: 47
> > 4K pages checked: 800709
> > 4K pages set-checked: 7668
> >
> > After:
> >
> > 1G pages checked: 2
> > 1G pages sameprot: 0
> > 1G pages preserved: 0
> > 2M pages checked: 538
> > 2M pages sameprot: 466
> > 2M pages preserved: 47
> > 4K pages checked: 560642
> > 4K pages set-checked: 7668
>
> With this new path added, I would have expected "2M pages sameprot" or
> "1G pages sameprot" to go up. The "checked" pages go down, which makes
> sense, but I don't see either of the "sameprot"s going up.
>
> I did a quick look back at the stats patch and didn't see any obvious
> buglets that can account for it. Both that and this code look sane, but
> the stats just don't seem to square for some reason.
sameprot does not go up, because the change merily leaves early when it
detected the same prot and full mapping size. So it really just avoids the
extra scanning of the large pages in 4k steps which obviously does not come
to a different conclusion. So quite the contrary if the same prot count
would go up then the early dropout would be wrong because the 4k loop finds
a violation.
Thanks,
tglx
next prev parent reply other threads:[~2018-09-27 18:07 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-17 14:29 [patch V3 00/11] x86/mm/cpa: Improve large page preservation handling Thomas Gleixner
2018-09-17 14:29 ` [patch V3 01/11] x86/mm/init32: Mark text and rodata RO in one go Thomas Gleixner
2018-09-21 16:15 ` Dave Hansen
2018-09-27 18:45 ` [tip:x86/mm] " tip-bot for Thomas Gleixner
2018-09-17 14:29 ` [patch V3 02/11] x86/mm/cpa: Split, rename and clean up try_preserve_large_page() Thomas Gleixner
2018-09-18 7:03 ` Peter Zijlstra
2018-09-18 8:19 ` Peter Zijlstra
2018-09-18 12:14 ` Peter Zijlstra
2018-09-18 22:34 ` Thomas Gleixner
2018-09-21 16:22 ` Dave Hansen
2018-09-27 18:46 ` [tip:x86/mm] " tip-bot for Thomas Gleixner
2018-09-17 14:29 ` [patch V3 03/11] x86/mm/cpa: Rework static_protections() Thomas Gleixner
2018-09-21 16:33 ` Dave Hansen
2018-09-27 18:46 ` [tip:x86/mm] " tip-bot for Thomas Gleixner
2018-09-17 14:29 ` [patch V3 04/11] x86/mm/cpa: Allow range check for static protections Thomas Gleixner
2018-09-21 16:36 ` Dave Hansen
2018-09-27 18:47 ` [tip:x86/mm] " tip-bot for Thomas Gleixner
2018-09-17 14:29 ` [patch V3 05/11] x86/mm/cpa: Add debug mechanism Thomas Gleixner
2018-09-21 16:40 ` Dave Hansen
2018-09-22 10:33 ` Peter Zijlstra
2018-09-27 18:48 ` [tip:x86/mm] " tip-bot for Thomas Gleixner
2018-09-17 14:29 ` [patch V3 06/11] x86/mm/cpa: Add large page preservation statistics Thomas Gleixner
2018-09-21 19:59 ` Dave Hansen
2018-09-27 18:48 ` [tip:x86/mm] " tip-bot for Thomas Gleixner
2018-09-17 14:29 ` [patch V3 07/11] x86/mm/cpa: Avoid static protection checks on unmap Thomas Gleixner
2018-09-21 20:01 ` Dave Hansen
2018-09-27 18:49 ` [tip:x86/mm] " tip-bot for Thomas Gleixner
2018-09-17 14:29 ` [patch V3 08/11] x86/mm/cpa: Add sanity check for existing mappings Thomas Gleixner
2018-09-18 7:14 ` Peter Zijlstra
2018-09-21 20:07 ` Dave Hansen
2018-09-27 18:49 ` [tip:x86/mm] " tip-bot for Thomas Gleixner
2018-09-17 14:29 ` [patch V3 09/11] x86/mm/cpa: Optimize same protection check Thomas Gleixner
2018-09-21 20:12 ` Dave Hansen
2018-09-27 18:07 ` Thomas Gleixner [this message]
2018-09-27 18:50 ` [tip:x86/mm] " tip-bot for Thomas Gleixner
2018-09-17 14:29 ` [patch V3 10/11] x86/mm/cpa: Do the range check early Thomas Gleixner
2018-09-21 20:26 ` Dave Hansen
2018-09-27 18:50 ` [tip:x86/mm] " tip-bot for Thomas Gleixner
2018-09-17 14:29 ` [patch V3 11/11] x86/mm/cpa: Avoid the 4k pages check completely Thomas Gleixner
2018-09-21 20:32 ` Dave Hansen
2018-09-27 18:51 ` [tip:x86/mm] " tip-bot for Thomas Gleixner
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