Re: [PATCH] [12/22] Remove GFP_DMAs/unchecked_isa_dma checks in scsi_scan.c

[Andi Kleen <andi@firstfloor.org>]

On Mon, Feb 25, 2008 at 07:04:20AM -0800, James Bottomley wrote:
> On Mon, 2008-02-25 at 15:58 +0100, Andi Kleen wrote:
> > On Mon, Feb 25, 2008 at 06:46:58AM -0800, James Bottomley wrote:
> > > 
> > > On Mon, 2008-02-25 at 00:35 +0100, Andi Kleen wrote:
> > > > Should not be needed because the block layer bounces that all.
> > > > 
> > > > Signed-off-by: Andi Kleen <ak@suse.de>
> > > > 
> > > > ---
> > > >  drivers/scsi/scsi_scan.c |    6 ++----
> > > >  1 file changed, 2 insertions(+), 4 deletions(-)
> > > > 
> > > > Index: linux/drivers/scsi/scsi_scan.c
> > > > ===================================================================
> > > > --- linux.orig/drivers/scsi/scsi_scan.c
> > > > +++ linux/drivers/scsi/scsi_scan.c
> > > > @@ -1010,8 +1010,7 @@ static int scsi_probe_and_add_lun(struct
> > > >  	if (!sdev)
> > > >  		goto out;
> > > >  
> > > > -	result = kmalloc(result_len, GFP_ATOMIC |
> > > > -			((shost->unchecked_isa_dma) ? __GFP_DMA : 0));
> > > > +	result = kmalloc(result_len, GFP_ATOMIC);
> > > >  	if (!result)
> > > >  		goto out_free_sdev;
> > > >  
> > > > @@ -1328,8 +1327,7 @@ static int scsi_report_lun_scan(struct s
> > > >  	 * prevent us from finding any LUNs on this target.
> > > >  	 */
> > > >  	length = (max_scsi_report_luns + 1) * sizeof(struct scsi_lun);
> > > > -	lun_data = kmalloc(length, GFP_ATOMIC |
> > > > -			   (sdev->host->unchecked_isa_dma ? __GFP_DMA : 0));
> > > > +	lun_data = kmalloc(length, GFP_ATOMIC);
> > > >  	if (!lun_data) {
> > > >  		printk(ALLOC_FAILURE_MSG, __FUNCTION__);
> > > >  		goto out;
> > > 
> > > Andi, this can't be right.
> > 
> > You mean it is incorrect or just not optimal? 
> 
> It's not optimal ... but that's sufficient an objection.
> 
> > > 
> > > You're removing something that's actually useful.  I'm happy to
> > > substitute this kmalloc for kmalloc_mask on the device dma mask which
> > > will do the same thing and so junk unchecked_isa_dma() that way (and
> > > actually fix us up for other weird mask devices), but just using
> > > ZONE_NORMAL is wrong because we'll then bounce all the time for
> > > something we knew a priori how to avoid.
> > 
> > That would require adding a separate mask just for this to the 
> > template. I figured the SCSI scan was not performance critical
> > so a few more copies just for this case was an ok trade off
> > for simpler code.
> 
> Why?  We already have the device; can't we just use its mask?

These ISA drivers I worked with definitely don't know 
anything about a device in any form.

Also there is the issue that 50+% of the ISA drivers actually
don't need it even if they had a ISA device.

> 
> > You think it makes sense to optimize scsi scan?
> 
> It makes sense to use information we already know to optimise the path,

In this case we would need to add a special new field for this
to the SCSI template (assume unchecked_isa_dma is already gone). 
You think that is worth it? 

-Andi