linux-kernel - Re: [PATCH] mm, vmacache: Add kconfig VMACACHE

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Message-ID: <54C123CF.2070107@redhat.com>
Date:	Thu, 22 Jan 2015 11:22:39 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Davidlohr Bueso <dave@...olabs.net>,
	WANG Chao <chaowang@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Michel Lespinasse <walken@...gle.com>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, vmacache: Add kconfig VMACACHE_SHIFT

On 01/22/2015 11:19 AM, Davidlohr Bueso wrote:
> On Thu, 2015-01-22 at 15:57 +0800, WANG Chao wrote:
>> Hi, Davidlohr
>>
>> On 01/21/15 at 11:46pm, Davidlohr Bueso wrote:
>>> On Thu, 2015-01-22 at 14:29 +0800, WANG Chao wrote:
>>>> Add a new kconfig option VMACACHE_SHIFT (as a power of 2) to specify the
>>>> number of slots vma cache has for each thread. Range is chosen 0-4 (1-16
>>>> slots) to consider both overhead and performance penalty. Default is 2
>>>> (4 slots) as it originally is, which provides good enough balance.
>>>>
>>>
>>> Nack. I don't feel comfortable making scalability features of core code
>>> configurable.
>>
>> Out of respect, is this a general rule not making scalability features
>> of core code configurable?
> 
> I doubt its a rule, just common sense. Users have no business
> configuring such low level details. The optimizations need to
> transparently work for everyone.

There may sometimes be a good reason for making this kind of
thing configurable, but since there were no performance
numbers in the changelog, I have not seen any such reason for
this particular change :)
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