Re: [PATCH 0/3] map multiple blocks in get_block() and mpage_readpages()

[Suparna Bhattacharya <suparna@in.ibm.com>]

On Fri, Feb 24, 2006 at 09:19:08AM -0800, Badari Pulavarty wrote:
> 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 ?

With 64K page size that could include 4K, 8K, 16K, 32K block size filesystems
as well, not sure how likely that would be ?

Regards
Suparna

> 	
> Thanks,
> Badari
> 
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-- 
Suparna Bhattacharya (suparna@in.ibm.com)
Linux Technology Center
IBM Software Lab, India