linux-kernel - Re: [PATCH] mm: remove global locks from mm/highmem.c

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Date:	Wed, 31 Jan 2007 11:44:36 +1100
From:	David Chinner <dgc@....com>
To:	Andrew Morton <akpm@...l.org>
Cc:	"Martin J. Bligh" <mbligh@...igh.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ingo Molnar <mingo@...e.hu>, David Chinner <dgc@....com>
Subject: Re: [PATCH] mm: remove global locks from mm/highmem.c

On Mon, Jan 29, 2007 at 06:15:57PM -0800, Andrew Morton wrote:
> We still don't know what is the source of kmap() activity which
> necessitated this patch btw.  AFAIK the busiest source is ext2 directories,
> but perhaps NFS under certain conditions?
> 
> <looks at xfs_iozero>
> 
> ->prepare_write no longer requires that the caller kmap the page.

Agreed, but don't we (xfs_iozero) have to map it first to zero it?

I think what you are saying here, Andrew, is that we can
do something like:

	page = grab_cache_page
	->prepare_write(page)
	kaddr = kmap_atomic(page, KM_USER0)
	memset(kaddr+offset, 0, bytes)
	flush_dcache_page(page)
	kunmap_atomic(kaddr, KM_USER0)
	->commit_write(page)

to avoid using kmap() altogether?

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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