linux-kernel - Re: [PATCH v5 6/7] x86/tlb: optimizing flush_tlb

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Message-ID: <CAPa8GCDgg9EUKvDHXtybBKtBhbRK-NAALR5f7+UU=S6XvPL_cw@mail.gmail.com>
Date:	Tue, 15 May 2012 20:06:54 +1000
From:	Nick Piggin <npiggin@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Alex Shi <alex.shi@...el.com>, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, arnd@...db.de,
	rostedt@...dmis.org, fweisbec@...il.com, jeremy@...p.org,
	riel@...hat.com, luto@....edu, avi@...hat.com, len.brown@...el.com,
	dhowells@...hat.com, fenghua.yu@...el.com, borislav.petkov@....com,
	yinghai@...nel.org, ak@...ux.intel.com, cpw@....com,
	steiner@....com, akpm@...ux-foundation.org, penberg@...nel.org,
	hughd@...gle.com, rientjes@...gle.com,
	kosaki.motohiro@...fujitsu.com, n-horiguchi@...jp.nec.com,
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	kamezawa.hiroyu@...fujitsu.com, viro@...iv.linux.org.uk,
	linux-kernel@...r.kernel.org, yongjie.ren@...el.com,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH v5 6/7] x86/tlb: optimizing flush_tlb_mm

On 15 May 2012 20:00, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> On Tue, 2012-05-15 at 19:52 +1000, Nick Piggin wrote:
>>
>> It could be warranted to change tlb_flush_mmu to a range API to
>> avoid doing the per-entry tracking which those architectures do?
>
> The per-entry could result in a much smaller range, there's no point in
> flushing tlbs for unpopulated pages.

Well common case for small ranges hopefully would be quite dense
I think. It could be not worth the extra work (although maybe it would
be).

>
> Anyway, I don't think even think we'd need to change the API for that,
> you could track the entire range through tlb_start_vma() if you wanted
> (although nobody does that IIRC).

I'm not sure if you can do that very well, because the tlb might have to
be flushed part way through a vma when we fill up the gather, so you
don't want to flush the full range each time.
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