linux-kernel - Re: [patch] rd: support XIP

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Message-ID: <20071204113549.GA6751@wotan.suse.de>
Date:	Tue, 4 Dec 2007 12:35:49 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Christian Borntraeger <borntraeger@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>, rob@...dley.net,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [patch] rd: support XIP

On Tue, Dec 04, 2007 at 03:26:20AM -0800, Andrew Morton wrote:
> On Tue, 4 Dec 2007 12:21:00 +0100 Nick Piggin <npiggin@...e.de> wrote:
> 
> > +	 *
> > +	 * Cannot support XIP and highmem, because our ->direct_access
> > +	 * routine for XIP must return memory that is always addressable.
> > +	 * If XIP was reworked to use pfns and kmap throughout, this
> > +	 * restriction might be able to be lifted.
> >  	 */
> > +	gfp_flags = GFP_NOIO | __GFP_ZERO;
> > +#ifndef CONFIG_BLK_DEV_XIP
> > +	gfp_flags |= __GFP_HIGHMEM;
> > +#endif
> 
> A dubious tradeoff?

On big highmem machines certainly. It may be somewhat useful on small
memory systems... but having the config option there is nice for a VM
developer without an s390 easily available ;)

But don't apply these XIP patches yet -- after a bit more testing I'm
seeing some data corruption, so I'll have to work out what's going
wrong with that first.
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