Date: Mon, 9 Oct 2006 14:14:17 +0200
From: Nick Piggin <npiggin@suse.de>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Andrew Morton <akpm@osdl.org>,
       Linux Memory Management <linux-mm@kvack.org>,
       Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [patch 3/3] mm: fault handler to replace nopage and populate
Message-ID: <20061009121417.GA3785@wotan.suse.de>
References: <20061009102635.GC3487@wotan.suse.de> <1160391014.10229.16.camel@localhost.localdomain> <20061009110007.GA3592@wotan.suse.de> <1160392214.10229.19.camel@localhost.localdomain> <20061009111906.GA26824@wotan.suse.de> <1160393579.10229.24.camel@localhost.localdomain> <20061009114527.GB26824@wotan.suse.de> <1160394571.10229.27.camel@localhost.localdomain> <20061009115836.GC26824@wotan.suse.de> <1160395671.10229.35.camel@localhost.localdomain>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1160395671.10229.35.camel@localhost.localdomain>
User-Agent: Mutt/1.5.9i
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1475
Lines: 26

On Mon, Oct 09, 2006 at 10:07:50PM +1000, Benjamin Herrenschmidt wrote:
> On Mon, 2006-10-09 at 13:58 +0200, Nick Piggin wrote:
> > 
> > The VM won't see that you have struct pages backing the ptes, and won't
> > do the right refcounting or rmap stuff... But for file backed mappings,
> > all the critical rmap stuff should be set up at mmap time, so you might
> > have another option to simply always do the nopfn thing, as far as the
> > VM is concerned (ie. even when you do have a struct page)
> 
> Any reason why it wouldn't work to flip that bit on the first no_page()
> after a migration ? A migration always involves destroying all PTEs and
> is done with a per-object mutex held that no_page() takes too, so we can
> be pretty sure that the first nopage can set that bit before any PTE is
> actually inserted in the mapping after all the previous ones have been
> invalidated... That would avoid having to walk the vma's.

Ok I guess that would work. I was kind of thinking that one needs to
hold the mmap_sem for writing when changing the flags, but so long
as everyone *else* does, then I guess you can get exclusion from just
the read lock. And your per-object mutex would prevent concurrent
nopages from modifying it.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/