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