linux-kernel - Re: Execute in place

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Message-ID: <Pine.LNX.4.64.0705021616260.31229@blonde.wat.veritas.com>
Date:	Wed, 2 May 2007 16:22:43 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Björn Steinbrink <B.Steinbrink@....de>
cc:	Phillip Susi <psusi@....rr.com>,
	Linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Execute in place

On Wed, 2 May 2007, Björn Steinbrink wrote:
> On 2007.05.02 15:04:44 +0100, Hugh Dickins wrote:
> > On Tue, 1 May 2007, Phillip Susi wrote:
> > > I seem to remember seeing some patches go by at some point that
> > > allowed one of the rom type embeded system filesystems to directly
> > > execute binaries out of the original rom memory rather than copying
> > > them to ram first, then executing from there.  I was wondering if
> > > rootfs or tmpfs support such execute in place today, or if binaries
> > > executed from there have their code segments duplicated in ram?
> > 
> > Only ext2 supports it today: see Documentation/filesystems/xip.txt
> 
> As I understand it, xip avoids the page cache copy. But tmpfs already
> lives in the page cache (or swap), so avoiding that "copy" is
> impossible. But I always expected tmpfs to implicitly due its own kind
> of xip, i.e. that it doesn't have to store its stuff in the page cache
> twice. Are you saying that this isn't true?

tmpfs doesn't store its stuff in the page cache twice: that's true,
and I didn't mean to imply otherwise.  But tmpfs doesn't contain any
support for rom memory: you'd have to copy from rom to tmpfs to use it.

Hugh