Re: [RFC 4/8] scsi-ml: scsi_sgtable implementation

[FUJITA Tomonori <tomof@acm.org>]

From: Mike Christie <michaelc@cs.wisc.edu>
Subject: Re: [RFC 4/8] scsi-ml: scsi_sgtable implementation
Date: Thu, 12 Jul 2007 14:09:44 -0500

> Boaz Harrosh wrote:
> > +/*
> > + * Should fit within a single page.
> > + */
> > +enum { SCSI_MAX_SG_SEGMENTS =
> > +	((PAGE_SIZE - sizeof(struct scsi_sgtable)) /
> > +	sizeof(struct scatterlist)) };
> > +
> > +enum { SG_MEMPOOL_NR =
> > +	(SCSI_MAX_SG_SEGMENTS >= 7) +
> > +	(SCSI_MAX_SG_SEGMENTS >= 15) +
> > +	(SCSI_MAX_SG_SEGMENTS >= 31) +
> > +	(SCSI_MAX_SG_SEGMENTS >= 63) +
> > +	(SCSI_MAX_SG_SEGMENTS >= 127) +
> > +	(SCSI_MAX_SG_SEGMENTS >= 255) +
> > +	(SCSI_MAX_SG_SEGMENTS >= 511)
> > +};
> >  
> 
> What does SCSI_MAX_SG_SEGMENTS end up being on x86 now? On x86_64 or 
> some other arch, we were going over a page when doing 
> SCSI_MAX_PHYS_SEGMENTS of 256 right?

Seems that 170 with x86 and 127 with x86_64.


> What happened to Jens's scatter list chaining and how does this relate 
> to it then?

With Jens' sglist, we can set SCSI_MAX_SG_SEGMENTS to whatever we
want. We can remove the above code.

We need to push this and Jens' sglist together in one merge window, I
think.