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Date: Fri, 27 Sep 2002 12:58:00 -0700
From: Andrew Morton <akpm@digeo.com>
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Subject: Re: Warning - running *really* short on DMA buffers while 
 doingfiletransfers
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Andrew Morton wrote:
> 
> ...
> One sample trace is at
> http://www.zip.com.au/~akpm/linux/patches/trace.txt
> 

Another thing to note from that trace is that many writes
went through the entire submit_bio/elv_next_request/bio_endio
cycle between the submission and completion of the read.

So there was:

	submit_bio(the read)
	elv_next_request(the read)
	...
	submit_bio(a write)
	elv_next_request(that write)
	bio_endio(that write)
	...
	bio_endio(the read)

For many writes.  I'm fairly (but not 100%) sure that the same
behaviour was seen with four tags.