On Fri, Apr 27 2007, Nick Piggin wrote:
> Why do we limit drivers to 128 sg entries?
No particular reason, except than to avoid 2^bigger order allocations.
2MiB requests would require 3 contig pages to setup the sg list, which
is (probably) a little troublesome especially since it's sometimes
atomically allocated.
Larger pages are by no means a prerequisite to getting larger requests,
assuming your hardware can handle the bigger sglist. There are other
ways of doing that, I've contemplated doing chained sglists and adding
sg_for_each_segment() macros for iterating these things. Drivers that
want larger sglists would then be required to update their sg mapping
loop to use the provided macros. It wouldn't be too hard.
--
Jens Axboe
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