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

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Message-ID: <20091218184504.GA675@elte.hu>
Date:	Fri, 18 Dec 2009 19:45:04 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	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.


* 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.

( You brought up -rt but that example does not apply: it doesnt 'hide' the 
  lock instance in any way, it simply changes the preemption model. It goes to 
  great lengths to keep existing locking patterns and does not obfuscate 
  locking. )

	Ingo
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