linux-kernel - Re: [PATCH 5/7] x86: mm: new tunable for single vs full TLB flush

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Message-ID: <5319FF8D.1080107@sr71.net>
Date:	Fri, 07 Mar 2014 09:19:09 -0800
From:	Dave Hansen <dave@...1.net>
To:	Davidlohr Bueso <davidlohr@...com>
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	ak@...ux.intel.com, kirill.shutemov@...ux.intel.com,
	mgorman@...e.de, alex.shi@...aro.org, x86@...nel.org,
	linux-mm@...ck.org, dave.hansen@...ux.intel.com
Subject: Re: [PATCH 5/7] x86: mm: new tunable for single vs full TLB flush

On 03/06/2014 05:37 PM, Davidlohr Bueso wrote:
> On Wed, 2014-03-05 at 16:45 -0800, Dave Hansen wrote:
>> From: Dave Hansen <dave.hansen@...ux.intel.com>
>> +
>> +If you believe that invlpg is being called too often, you can
>> +lower the tunable:
>> +
>> +	/sys/debug/kernel/x86/tlb_single_page_flush_ceiling
>> +
> 
> Whenever this tunable needs to be updated, most users will not know what
> a invlpg is and won't think in terms of pages either. How about making
> this in units of Kb instead? But then again most of those users won't be
> looking into tlb flushing issues anyways, so...

Yeah, talking about the instruction directly in the documentation is
probably going a bit far.  I'll see if I can uplevel it a bit.

It's obviously not a big deal to change it to be pages vs. kb, but for
something that's as *COMPLETELY* developer-focused, I think we can keep
it in pages.  We don't want users fooling with this.

> While obvious, tt should also mention that this does not apply to
> hugepages.

Good point.

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