linux-kernel - Re: [mm][RFC][PATCH 0/11] mm accessor updates.

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Message-ID: <339143df87bf5d7afe89b9b2fe8af031.squirrel@webmail-b.css.fujitsu.com>
Date:	Sat, 19 Dec 2009 08:18:33 +0900 (JST)
From:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Christoph Lameter" <cl@...ux-foundation.org>,
	"Avi Kivity" <avi@...hat.com>,
	"Peter Zijlstra" <peterz@...radead.org>,
	"Andi Kleen" <andi@...stfloor.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	minchan.kim@...il.com
Subject: Re: [mm][RFC][PATCH 0/11] mm accessor updates.

Ingo Molnar wrote:
>
> * Christoph Lameter <cl@...ux-foundation.org> wrote:
>
>> > We've been through this many times in the past within the kernel: many
>> > times when we hid some locking primitive within some clever wrapping
>> > scheme the quality of locking started to deteriorate. In most of the
>> > important cases we got rid of the indirection and went with an
>> existing
>> > core kernel locking primitive which are all well known and have clear
>> > semantics and lead to more maintainable code.
>>
>> The existing locking APIs are all hiding lock details at various levels.
>> We
>> have various specific APIs for specialized locks already Page locking
>> etc.
>
> You need to loo at the patches. This is simply a step backwards:
>
> -               up_read(&mm->mmap_sem);
> +               mm_read_unlock(mm);
>
> because it hides the lock instance.
>
After rewriting speculative-page-fault patches, I feel I can do it
without mm_accessor, by just skipping mmap_sem in fault.c. Then, original
problem I tried to fix, false sharing at multithread page fault, can be
fixed without this.

Then, I myself stop this.

About range-locking of mm_struct, I don't find any good approach.

Sorry for annoying and thank you all.
-Kame






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