linux-kernel - Re: [patch] fs: restore nobh

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Message-ID: <20071025190736.GB12883@atrey.karlin.mff.cuni.cz>
Date:	Thu, 25 Oct 2007 21:07:36 +0200
From:	Jan Kara <jack@...e.cz>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch] fs: restore nobh

  Hi,

> This is overdue, sorry. Got a little complicated, and I've been away from
> my filesystem test setup so I didn't want ot send it (lucky, coz I found
> a bug after more substantial testing).
> 
> Anyway, RFC?
  Hmm, maybe one comment/question:

> Index: linux-2.6/fs/buffer.c
> ===================================================================
> --- linux-2.6.orig/fs/buffer.c	2007-10-08 14:09:35.000000000 +1000
> +++ linux-2.6/fs/buffer.c	2007-10-08 16:45:28.000000000 +1000
...

> -/*
> - * Make sure any changes to nobh_commit_write() are reflected in
> - * nobh_truncate_page(), since it doesn't call commit_write().
> - */
> -int nobh_commit_write(struct file *file, struct page *page,
> -		unsigned from, unsigned to)
> +int nobh_write_end(struct file *file, struct address_space *mapping,
> +			loff_t pos, unsigned len, unsigned copied,
> +			struct page *page, void *fsdata)
>  {
>  	struct inode *inode = page->mapping->host;
> -	loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
> +	struct buffer_head *head = NULL;
> +	struct buffer_head *bh;
>  
> -	if (page_has_buffers(page))
> -		return generic_commit_write(file, page, from, to);
> +	if (!PageMappedToDisk(page)) {
> +		if (unlikely(copied < len) && !page_has_buffers(page))
> +			attach_nobh_buffers(page, head);
> +		if (page_has_buffers(page))
> +			return generic_write_end(file, mapping, pos, len, copied, page, fsdata);
> +	}
  So we can have a page with attached buffers but we decide to not call
generic_write_end()...

>  	SetPageUptodate(page);
>  	set_page_dirty(page);
  And we just set the page dirty but we leave buffers clean. So cannot
subsequent try_to_free_buffers() come, mark page as clean (as buffers
are clean) and discard the data?

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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