Re: 2.4.16: running *really* short on DMA buffers

Heinz-Ado Arnolds (Ado.Arnolds@dhm-systems.de)
Thu, 06 Dec 2001 10:45:16 +0100

Gérard Roudier wrote:
>
> On Wed, 5 Dec 2001, Heinz-Ado Arnolds wrote:
>
> > Hi all,
> >
> > I get the message "kernel: Warning - running *really* short on DMA
> > buffers" frequently with medium to heavy disk i/o (running several
> > tar and/or moving huge directories).
...
> So, they are the allocations internal to the scsi layer that may well
> exhaust the ISA DMA pool. This pool is divided into 512 bytes chunks.
> Under heavy reordering of IOs, it can get very fragmented and much memory
> being wasted as a result.
>
> An immediate solution might be to hack the scsi code for it to allocate
> more memory.

I'm not an experienced kernel hacker. Please help me: would it be right
to increase the constant 2 in

new_dma_sectors = 2 * SECTORS_PER_PAGE;
^
in drivers/scsi/scsi_dma.c, scsi_resize_dma_pool() to 3 or 4 as a first
solution. Or is there an other place I should start?

> The error string in well known since years, so you shouldn't have missed
> it from sources. :-)
Sorry, my stupid fault. For sure, it's in drivers/scsi/scsi_merge.c.

Thanks for your attention

Ado

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  Heinz-Ado Arnolds                        Ado.Arnolds@web-systems.net
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