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Running *really" short on DMA buffers

Posted on 2002-07-15
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Last Modified: 2010-04-20
This kernel message has begun to appear since updating from 2.4.18-4 to 2.4.18-5:
Warning - running *really* short on DMA buffers
I found this message in source file scsi_merge.c
Is this tunable type issue, or do I report a bug?
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Question by:medent
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by:jlevie
ID: 7155376
How much physical memory do you have in the system. It's possible that the problem could be a general memoryt shortage and not a kernel/driver problem.
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Expert Comment

by:coolestONE
ID: 7156630
I hope you are not using any ISA device. ISA devices do not use the standard DMA channels.
run the command $rcidedma status to check if DMA is working or not.
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by:medent
ID: 7156899
rcidedma? I am running redhat...is this part of a package?
amount of memory? On one server 512Megs, and 640Megs on the other server with this error (both 1Ghz IBM intel). The problem seems to happen during large file transfers (via rcp), with nothing else happening on the machine.
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by:coolestONE
ID: 7158628
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jlevie earned 250 total points
ID: 7158710
It seems rather obvious to me that the SCSI system in the 18-5 kernel is on the chatty side, compared to previous kernel versions. It may well be that nothing is wrong and that you are just seeing the increased verbosity of the driver.

The way I read the code it looks like this is more informative than an error. I think the message pops out when the SCSI subsystem is busy (lots of buffers in use) and it wants to coalese a scatter-gather IO into a single request. If that analysis is correct it just means that the SCSI subsystem is running pretty much full bore for the controllers and devices that it has.
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by:medent
ID: 7159247
Excellent point. I am seeing a considerable amount of annoying informational scsi messaging that I did not see before. I will try to report via bugzilla (redhat) for wahtever that is worth. PS- I've deselected scsi verbosity from the kernel options, but no diff. Any tips on where to find out if "bugs" like this are being worked on?
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by:jlevie
ID: 7161145
I'll ask around and see if I can turn up anything.
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