Re: Couldn't get a free page

Richard B. Johnson (
Mon, 10 Mar 1997 14:59:04 -0500 (EST)

On Mon, 10 Mar 1997, Leonard N. Zubkoff wrote:

> Date: Mon, 10 Mar 1997 09:18:47 -0500 (EST)
> From: "Richard B. Johnson" <>
> Hello memory manager wizards........
> What #define do I change and were to get some more pages for Disc I/O?
> I can't write a large amount of data to a raw SCSI device for testing.
> I use the BusLogic driver. It gets memory for "DMA" from the kernel.
> It runs out and hangs.
> The BusLogic driver itself should never hang waiting for DMA memory. The only
> place it asks for memory after initialization is if it decides to expand the
> number of CCBs. In that case, it calls with GFP_ATOMIC and should handle not
> being able to create any.
> I would think the DMA memory allocations are coming from the SCSI disk driver
> itself (sd.c). I think there are some magic files in /proc that can reserve
> more free pages, but I've never tried them.
> Leonard

Okay. I'll check some more. I am trying to isolate a possible file-system
problem that occurs with _VERY_LARGE_ files. To isolate specific file-systems
I am trying to write to a raw SCSI device just to make sure I can read
what I write, i.e., is it a driver problem instead of a file-system problem.
So far, I can't write directly to the raw device without a "free-page" hang.

This may not be a problem in the "real" world because the kernel will get
a chance to free up FS buffers to make more free pages. However, when I
don't have the file-system cache, the SCSI interface has got to have
enough buffers to fill it's cached-write SCB queue.

Dick Johnson
Richard B. Johnson
Project Engineer
Analogic Corporation
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