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Date: Tue, 4 Dec 2007 12:35:49 +0100
From: Nick Piggin <npiggin@suse.de>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       linux-fsdevel@vger.kernel.org,
       "Eric W. Biederman" <ebiederm@xmission.com>, rob@landley.net,
       Jens Axboe <axboe@kernel.dk>
Subject: Re: [patch] rd: support XIP
Message-ID: <20071204113549.GA6751@wotan.suse.de>
References: <20071204042628.GA26636@wotan.suse.de> <200712041054.51599.borntraeger@de.ibm.com> <20071204101009.GB9618@wotan.suse.de> <20071204112100.GA20420@wotan.suse.de> <20071204032620.aaee039b.akpm@linux-foundation.org>
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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@suse.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.