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Date: Wed, 26 Sep 2001 15:22:01 -0300 (BRT)
From: Marcelo Tosatti <marcelo@conectiva.com.br>
To: Pavel Machek <pavel@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Daniel Phillips <phillips@bonn-fries.net>,
        Rob Fuller <rfuller@nsisoftware.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: broken VM in 2.4.10-pre9
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On Tue, 25 Sep 2001, Pavel Machek wrote:

> Hi!
> 
> > > So my suggestion was to look at getting anonymous pages backed by what
> > > amounts to a shared memory segment.  In that vein.  By using an extent
> > > based data structure we can get the cost down under the current 8 bits
> > > per page that we have for the swap counts, and make allocating swap
> > > pages faster.  And we want to cluster related swap pages anyway so
> > > an extent based system is a natural fit.
> >
> > Much of this goes away if you get rid of both the swap and anonymous page
> > special cases. Back anonymous pages with the "whoops everything I write here
> > vanishes mysteriously" file system and swap with a swapfs
> 
> What exactly is anonymous memory? I thought it is what you do when you
> want to malloc(), but you want to back that up by swap, not /dev/null.

Anonymous memory is memory which is not backed by a filesystem or a
device. eg: malloc()ed memory, shmem, mmap(MAP_PRIVATE) on a file (which
will create anonymous memory as soon as the program which did the mmap
writes to the mapped memory (COW)), etc.