linux-kernel - Re: [RFC 4/8] Enhance fallback functions in libs to support higher order pages

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Date:	Fri, 20 Apr 2007 12:05:17 +0100
From:	mel@...net.ie (Mel Gorman)
To:	Christoph Lameter <clameter@....com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <nickpiggin@...oo.com.au>, Andi Kleen <ak@...e.de>,
	Paul Jackson <pj@....com>, Dave Chinner <dgc@....com>,
	shaggy@...ux.vnet.ibm.com
Subject: Re: [RFC 4/8] Enhance fallback functions in libs to support higher order pages

On (19/04/07 09:35), Christoph Lameter didst pronounce:
> Variable Order Page Cache: Fixup fallback functions
> 
> Fixup the fallback function in fs/libfs.c to be able to handle
> higher order page cache pages.
> 
> Signed-off-by: Christoph Lameter <clameter@....com>
> 
> ---
>  fs/libfs.c |   16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> Index: linux-2.6.21-rc7/fs/libfs.c
> ===================================================================
> --- linux-2.6.21-rc7.orig/fs/libfs.c	2007-04-18 21:52:49.000000000 -0700
> +++ linux-2.6.21-rc7/fs/libfs.c	2007-04-18 21:54:51.000000000 -0700
> @@ -320,8 +320,8 @@ int simple_rename(struct inode *old_dir,
>  
>  int simple_readpage(struct file *file, struct page *page)
>  {
> -	clear_highpage(page);
> -	flush_dcache_page(page);
> +	clear_mapping_page(file->f_mapping, page);
> +	flush_mapping_page(file->f_mapping, page);

right, I think it would be easier to read if patches 3 and 4 were
merged. Personal preference, feel free to ignore

>  	SetPageUptodate(page);
>  	unlock_page(page);
>  	return 0;
> @@ -331,11 +331,15 @@ int simple_prepare_write(struct file *fi
>  			unsigned from, unsigned to)
>  {
>  	if (!PageUptodate(page)) {
> -		if (to - from != PAGE_CACHE_SIZE) {
> +		if (to - from != page_cache_size(file->f_mapping)) {
> +			/*
> +			 * Mapping to higher order pages need to be supported
> +			 * if higher order pages can be in highmem
> +			 */

comments about missing page_cache_size() covered elsewhere. However, I
note that Dave Kleikamp might be interested in this changing of
page_cache_size() from the perspective of page cache tails. I've added
him to the cc so he can take a quick look.

>  			void *kaddr = kmap_atomic(page, KM_USER0);
>  			memset(kaddr, 0, from);
> -			memset(kaddr + to, 0, PAGE_CACHE_SIZE - to);
> -			flush_dcache_page(page);
> +			memset(kaddr + to, 0, page_cache_size(file->f_mapping) - to);
> +			flush_mapping_page(file->f_mapping, page);
>  			kunmap_atomic(kaddr, KM_USER0);
>  		}
>  	}
> @@ -346,7 +350,7 @@ int simple_commit_write(struct file *fil
>  			unsigned from, unsigned to)
>  {
>  	struct inode *inode = page->mapping->host;
> -	loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
> +	loff_t pos = ((loff_t)page->index << page_cache_shift(file->f_mapping)) + to;
>  
>  	if (!PageUptodate(page))
>  		SetPageUptodate(page);
> -
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-- 
-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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