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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH -mm 14/24] Ramfs and Ram Disk pages are unevictable
Date: Fri, 13 Jun 2008 03:37:56 +1000
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Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       Lee Schermerhorn <lee.schermerhorn@hp.com>,
       Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>, linux-mm@kvack.org,
       Eric Whitney <eric.whitney@hp.com>
References: <20080611184214.605110868@redhat.com> <200806121054.19253.nickpiggin@yahoo.com.au> <20080612132952.568226f6@cuia.bos.redhat.com>
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On Friday 13 June 2008 03:29, Rik van Riel wrote:
> On Thu, 12 Jun 2008 10:54:18 +1000
>
> Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> > On Thursday 12 June 2008 04:42, Rik van Riel wrote:
> > > From: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
> > >
> > > Christoph Lameter pointed out that ram disk pages also clutter the
> > > LRU lists.  When vmscan finds them dirty and tries to clean them,
> > > the ram disk writeback function just redirties the page so that it
> > > goes back onto the active list.  Round and round she goes...
> >
> > This isn't the case for brd any longer. It doesn't use the buffer
> > cache as its backing store, so the buffer cache is reclaimable.
>
> What does that mean?

That your patch is obsolete.


> I know that pages of files that got paged into the page
> cache from the ramdisk can be evicted (back to the ram
> disk), but how do the brd pages themselves behave?

They are not reclaimable. But they have nothing (directly) to do
with brd's i_mapping address space, nor are they put on any LRU
lists.