Re: [PATCH] Avoiding fragmentation through different allocator

[Andi Kleen <ak@muc.de>]

On Tue, Jan 25, 2005 at 02:27:57PM +0000, Christoph Hellwig wrote:
> > It is not the driver per se, but the way the memory which is the I/O
> > source/target is presented to the driver. In linux there is a good
> > chance it will have to use more scatter gather elements to represent
> > the same amount of data.
> 
> Note that a change made a few month ago after seeing issues with
> aacraid means it's much more likely to see contingous memory,
> there were some numbers on linux-scsi and/or linux-kernel.

But only at the beginning. iirc after a few days of uptime 
and memory fragmentation it degenerates back to the old numbers.

Perhaps the recent anti defragmentation work will help more.

-Andi

P.S.: on a AMD x86-64 box the theory can be relatively easily tested:
just run with iommu=force,biomerge that will use the IOMMU to merge
SG elements.  I just don't recommend it for production because some errors 
are not well handled.
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