Re: [PATCH, RFC] map multiple blocks at a time in mpage_readpage(s)

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

On Thu, Oct 20, 2005 at 03:06:31PM -0700, Andrew Morton wrote:
> Christoph Hellwig <hch@lst.de> wrote:
> >
> > On Tue, Oct 04, 2005 at 09:42:46PM +0200, Christoph Hellwig wrote:
> >  > This patch changes mpage_readpage/mpage_readpages to use a get_blocks
> >  > call that gets the disk mapping information for multiple blocks at the
> >  > same time, similar to the way direct I/O code works.  For extent based
> >  > filesystems like jfs, xfs or reiser4 this allows to reduce the overhead
> >  > of the allocator calls, which is especially nice when that codepath
> >  > is rather heavyweight (as it is for example in xfs).  For filesystems
> >  > that don't have an allocator that make use of it nothing changes.
> >  > 
> >  > I've tested this heavily on XFS with block size = page size and 512 byte
> >  > blocks, and it passes the XFS QA regression test suite fine.  I've done
> >  > some basic fsx testing on all the other affected filesystems.
> > 
> >  I think the patch should go into -mm after no one had serious objections.
> 
> It adds a bunch of complexity and overhead which will speed up a filesystem
> which few people use while slowing down the filesystems which most people
> use.
> 
> If/when we have an ext3 implementation of get_blocks() and some benchmarks
> which show it's worthwhile then OK.

We do already have this based on reservation based allocation (Mingming
posted the patches a while back). I think we need to combine the work we did
for mpage_writepages with the readpages work.

> 
> Could we please see the xfs benchmark results?
> 
> first_logical_block should have type sector_t.
> 
> Did you consider aggregating those nine args to do_mpage_readpage() into a
> struct, passing the address of that?

Regards
Suparna

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