linux-kernel - Re: [PATCH 00/11] V4: rwsem changes + down_read

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Message-ID: <20100527110210.GB20625@google.com>
Date:	Thu, 27 May 2010 04:02:10 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Waychison <mikew@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH 00/11] V4: rwsem changes + down_read_critical() proposal

On Wed, May 26, 2010 at 10:23:59AM +0900, KAMEZAWA Hiroyuki wrote:
> On Tue, 25 May 2010 11:27:55 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> > Also, do you really think doing something like:
> > 
> >         /*
> >          * Check the vma index is within the range and do
> >          * sequential scan until m_index.
> >          */
> >         vma = NULL;
> >         if ((unsigned long)l < mm->map_count) {
> >                 vma = mm->mmap;
> >                 while (l-- && vma)
> >                         vma = vma->vm_next;
> >                 goto out;
> >         }
> > 
> > with preemption disabled is a _good_ thing?
> > 
> > People were talking about raising our vma limit of 64k...

All right, this is clearly a problem then.

> Hmm..can't we use something speculative lookup for reading maps ?
> (as we played in several months ago...)

Would you happen to have a link to that conversation / remember the
subject line of the thread ?

Thanks,

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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