[PATCH 2.4.x] prevent emulated SCSI hosts from wasting DMA memory

[PATCH 2.4.x] prevent emulated SCSI hosts from wasting DMA memory

[Dan Aloni]

Emulated scsi hosts don't do DMA, so don't unnecessarily increase
the SCSI DMA pool.

Signed-off-by: Dan Aloni <da-x@monatomic.org>

---
commit 8f6409c7c270038ca4d154551e061f66a9580301
tree ab7fedd2e7dbaefe31c332fc487f45a005972571
parent a0837aece47b79a2bfd524e70e4f8a559c743c4c
author Dan Aloni <da-x@monatomic.org> Wed, 30 Nov 2005 18:14:11 +0200
committer Dan Aloni <da-x@monatomic.org> Wed, 30 Nov 2005 18:14:11 +0200

 drivers/scsi/scsi_dma.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/drivers/scsi/scsi_dma.c b/drivers/scsi/scsi_dma.c
index 5594828..52737d6 100644
--- a/drivers/scsi/scsi_dma.c
+++ b/drivers/scsi/scsi_dma.c
@@ -231,10 +231,17 @@ void scsi_resize_dma_pool(void)
 		need_isa_bounce_buffers = 0;
 
 	if (scsi_devicelist)
-		for (shpnt = scsi_hostlist; shpnt; shpnt = shpnt->next)
+		for (shpnt = scsi_hostlist; shpnt; shpnt = shpnt->next) {
+			if (shpnt->hostt->emulated)
+				continue;
+
 			new_dma_sectors += SECTORS_PER_PAGE;	/* Increment for each host */
+		}
 
 	for (host = scsi_hostlist; host; host = host->next) {
+		if (host->hostt->emulated)
+			continue;
+
 		for (SDpnt = host->host_queue; SDpnt; SDpnt = SDpnt->next) {
 			/*
 			 * sd and sr drivers allocate scatterlists.


-- 
Dan Aloni
da-x@monatomic.org, da-x@colinux.org, da-x@gmx.net

Re: [PATCH 2.4.x] prevent emulated SCSI hosts from wasting DMA memory

[Luke-Jr]

On Wednesday 30 November 2005 17:15, Dan Aloni wrote:
> Emulated scsi hosts don't do DMA, so don't unnecessarily increase
> the SCSI DMA pool.

They don't? Recently I learned(?) that apparently using hdparm -d on the 
old /dev/hdX device still worked/applied when using ide-scsi... or do 
"emulated scsi hosts" refer to something else?
-- 
Luke-Jr
Developer, Utopios
http://utopios.org/

Re: [PATCH 2.4.x] prevent emulated SCSI hosts from wasting DMA memory

[Dan Aloni]

On Wed, Nov 30, 2005 at 07:33:47PM +0000, Luke-Jr wrote:
> On Wednesday 30 November 2005 17:15, Dan Aloni wrote:
> > Emulated scsi hosts don't do DMA, so don't unnecessarily increase
> > the SCSI DMA pool.
> 
> They don't? Recently I learned(?) that apparently using hdparm -d on the 
> old /dev/hdX device still worked/applied when using ide-scsi... or do 
> "emulated scsi hosts" refer to something else?

Actually by 'do DMA' I meant use the scsi_malloc() interface - which 
is mostly used by low level drivers. The IDE drivers allocate their
DMA memory outside the SCSI layer. iSCSI hosts for instance, don't 
need to cause unnecessary DMA allocations.

-- 
Dan Aloni
da-x@monatomic.org, da-x@colinux.org, da-x@gmx.net

Re: [PATCH 2.4.x] prevent emulated SCSI hosts from wasting DMA memory

[Christoph Hellwig]

On Wed, Nov 30, 2005 at 11:02:23PM +0200, Dan Aloni wrote:
> On Wed, Nov 30, 2005 at 07:33:47PM +0000, Luke-Jr wrote:
> > On Wednesday 30 November 2005 17:15, Dan Aloni wrote:
> > > Emulated scsi hosts don't do DMA, so don't unnecessarily increase
> > > the SCSI DMA pool.
> > 
> > They don't? Recently I learned(?) that apparently using hdparm -d on the 
> > old /dev/hdX device still worked/applied when using ide-scsi... or do 
> > "emulated scsi hosts" refer to something else?
> 
> Actually by 'do DMA' I meant use the scsi_malloc() interface - which 
> is mostly used by low level drivers. The IDE drivers allocate their
> DMA memory outside the SCSI layer. iSCSI hosts for instance, don't 
> need to cause unnecessary DMA allocations.

(1) there's no guranteee a driver setting ->emulated can't use scsi_malloc
(2) 2.4.x is very late in the cycle so there's just no point in putting this
    in (and in 2.6.x scsi_malloc is gone fortunately)

Re: [PATCH 2.4.x] prevent emulated SCSI hosts from wasting DMA memory

[Dan Aloni]

On Thu, Dec 01, 2005 at 11:36:10AM +0000, Christoph Hellwig wrote:
> On Wed, Nov 30, 2005 at 11:02:23PM +0200, Dan Aloni wrote:
> > On Wed, Nov 30, 2005 at 07:33:47PM +0000, Luke-Jr wrote:
> > > On Wednesday 30 November 2005 17:15, Dan Aloni wrote:
> > > > Emulated scsi hosts don't do DMA, so don't unnecessarily increase
> > > > the SCSI DMA pool.
> > > 
> > > They don't? Recently I learned(?) that apparently using hdparm -d on the 
> > > old /dev/hdX device still worked/applied when using ide-scsi... or do 
> > > "emulated scsi hosts" refer to something else?
> > 
> > Actually by 'do DMA' I meant use the scsi_malloc() interface - which 
> > is mostly used by low level drivers. The IDE drivers allocate their
> > DMA memory outside the SCSI layer. iSCSI hosts for instance, don't 
> > need to cause unnecessary DMA allocations.
> 
> (1) there's no guranteee a driver setting ->emulated can't use scsi_malloc
> (2) 2.4.x is very late in the cycle so there's just no point in putting this
>     in (and in 2.6.x scsi_malloc is gone fortunately)

(1) you're right, the SCSI subsystem itself uses scsi_malloc(). But I 
wonder, would it be okay to simply replace scsi_malloc() invocations 
with kmalloc of GFP_ATOMIC and GFP_DMA? I mean, to take the relevant
bits out of the 2.5.1-pre11 patch and give it a shot?

(2) you are right again, but fact is that 2.4.x is still being used 
on some production systems for stability reasons (and also because 
the SCSI kernel interfaces in 2.6.x weren't stabilized yet).

More specifically, I've made that patch to be able to connect to 
a large number of iSCSI targets without problems. I wonder if 
there's another way for doing that instead of upgrading to 2.6.x.

-- 
Dan Aloni
da-x@monatomic.org, da-x@colinux.org, da-x@gmx.net

Re: [PATCH 2.4.x] prevent emulated SCSI hosts from wasting DMA memory

[Marcelo Tosatti]

On Thu, Dec 01, 2005 at 11:36:10AM +0000, Christoph Hellwig wrote:
> On Wed, Nov 30, 2005 at 11:02:23PM +0200, Dan Aloni wrote:
> > On Wed, Nov 30, 2005 at 07:33:47PM +0000, Luke-Jr wrote:
> > > On Wednesday 30 November 2005 17:15, Dan Aloni wrote:
> > > > Emulated scsi hosts don't do DMA, so don't unnecessarily increase
> > > > the SCSI DMA pool.
> > > 
> > > They don't? Recently I learned(?) that apparently using hdparm -d on the 
> > > old /dev/hdX device still worked/applied when using ide-scsi... or do 
> > > "emulated scsi hosts" refer to something else?
> > 
> > Actually by 'do DMA' I meant use the scsi_malloc() interface - which 
> > is mostly used by low level drivers. The IDE drivers allocate their
> > DMA memory outside the SCSI layer. iSCSI hosts for instance, don't 
> > need to cause unnecessary DMA allocations.
> 
> (1) there's no guranteee a driver setting ->emulated can't use scsi_malloc
> (2) 2.4.x is very late in the cycle so there's just no point in putting this
>     in (and in 2.6.x scsi_malloc is gone fortunately)

Agreed - this does not sound like a critical bug fix to me.