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

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Date:	Wed, 16 May 2012 23:09:29 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alex Shi <alex.shi@...el.com>
Cc:	Nick Piggin <npiggin@...il.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,
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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 Wed, 2012-05-16 at 21:34 +0800, Alex Shi wrote:
> 
> So, if the minimum change of tlb->start/end can be protected by
> HAVE_GENERIC_MMU_GATHER, it is safe and harmless, am I right?
> 
safe yes, but not entirely harmless. A quick look seems to suggest you
fail for VM_HUGETLB. If your mmu_gather spans a vma with VM_HUGETLB
you'll do a regular range flush not a full mm flush like the other paths
do.

Anyway, I did a quick refresh of my series on a recent -tip tree:

 git://git.kernel.org/pub/scm/linux/kernel/git/peterz/mmu.git tlb-unify

With that all you need is to "select HAVE_MMU_GATHER_RANGE" for x86 and
implement a useful flush_tlb_range().

In particular, see:
http://git.kernel.org/?p=linux/kernel/git/peterz/mmu.git;a=commitdiff;h=05e53144177e6242fda404045f50f48114bcf185;hp=2cd7dc710652127522392f4b7ecb5fa6e954941e

I've slightly changed the code to address an open issue with the
vm_flags tracking. We now force flush the mmu_gather whenever VM_HUGETLB
flips because most (all?) archs that look at that flag expect pure huge
pages and not a mixture.

I've seem to have misplaced my cross-compiler set, so I've only compiled
x86-64 for now.
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