Subject: Re: [PATCH 0/3] map multiple blocks in get_block() and
	mpage_readpages()
From: Badari Pulavarty <pbadari@us.ibm.com>
To: christoph <hch@lst.de>
Cc: mcao@us.ibm.com, akpm@osdl.org, lkml <linux-kernel@vger.kernel.org>,
       linux-fsdevel <linux-fsdevel@vger.kernel.org>, vs@namesys.com,
       zam@namesys.com
In-Reply-To: <20060222151216.GA22946@lst.de>
References: <1140470487.22756.12.camel@dyn9047017100.beaverton.ibm.com>
	 <20060222151216.GA22946@lst.de>
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Date: Fri, 24 Feb 2006 09:19:08 -0800
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On Wed, 2006-02-22 at 16:12 +0100, christoph wrote:
..
> Thanks Badari, with that interface changes the mpage_readpage changes
> look a lot nicer than my original version.  I'd like to second
> the request to put it into -mm. 
> 
> And if the namesys folks could try out whether this works for their
> reiser4 requirements it'd be nice.  If you have an even faster
> ->readpages I'd be interested in that secrete souce receipe for
> further improvement to mpage_readpages.

I don't have any secret receipes, but I was thinking of re-organizing
the code a little. Complexity is due to "confused" case and 
"blocksize < pagesize" cases + going in-and-out of the worker routine
with stored state.

I am thinking of having a "fast path" which doesn't deal with any
of those and "slow" path to deal with all that non-sense.
Something like ..

mpage_readpages()
{
	if (block-size < page-size)
		slow_path;

	while (nr-pages) {
		if (get_block(bh)) 
			slow_path;
		if (uptodate(bh))
			slow_path;
		while (bh.b_size) {
			if (not contig)
				submit bio();
			add all the pages we can to bio();
			bh.b_size -= size-of-pages-added;
			nr_pages -= count-of-pages-added;
		}

	}
}

slow_path is going to be slow & ugly. How important is to handle
1k, 2k filesystems efficiently ? Should I try ?
	
Thanks,
Badari

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