[PATCH v2 0/3] A few gup refactorings and documentation updates

[PATCH v2 0/3] A few gup refactorings and documentation updates

[John Hubbard]

OK, here is v2 with changes as recommended by Christoph Hellwig and
Matthew Wilcox (thanks!):

* Changed refs to @refs, and added some more documentation as well.

* Completely removed try_get_page(). (I'm adding more people and lists
to Cc, because of those call site changes.)

* Reversed the logic in try_grab_page() to make it a touch more
  readable.

Also, this has been rebased to today's linux-next (next-20210810), and
re-tested on that.

Here is the v1 cover letter, edited slightly to keep up with the latest
story.

While reviewing some of the other things going on around gup.c, I
noticed that the documentation was wrong for a few of the routines that
I wrote. And then I noticed that there was some significant code
duplication too. So this fixes those issues.

This is not entirely risk-free, but after looking closely at this, I
think it's actually a useful improvement, getting rid of the code
duplication here.

However, it is possible I've overlooked something. I did some local LTP
and other testing on an x86 test machine but failed to find any problems
yet.

And the original v1 is here:
https://lore.kernel.org/r/20210808235018.1924918-1-jhubbard@nvidia.com

John Hubbard (3):
  mm/gup: documentation corrections for gup/pup
  mm/gup: small refactoring: simplify try_grab_page()
  mm/gup: Remove try_get_page(), call try_get_compound_head() directly

 arch/s390/mm/fault.c |  2 +-
 fs/pipe.c            |  2 +-
 include/linux/mm.h   | 10 +-----
 mm/gup.c             | 79 ++++++++++++++++++++++----------------------
 4 files changed, 43 insertions(+), 50 deletions(-)

--
2.32.0

[PATCH v2 1/3] mm/gup: documentation corrections for gup/pup

[John Hubbard]

The documentation for try_grab_compound_head() and try_grab_page() has
fallen a little out of date. Update and clarify a few points.

Also make it kerneldoc-correct, by adding @args documentation.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 mm/gup.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 2630ed1bb4f4..52f08e3177e9 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -92,10 +92,17 @@ static inline struct page *try_get_compound_head(struct page *page, int refs)
 	return head;
 }
 
-/*
+/**
  * try_grab_compound_head() - attempt to elevate a page's refcount, by a
  * flags-dependent amount.
  *
+ * Even though the name includes "compound_head", this function is still
+ * appropriate for callers that have a non-compound @page to get.
+ *
+ * @page:  pointer to page to be grabbed
+ * @refs:  the value to (effectively) add to the page's refcount
+ * @flags: gup flags: these are the FOLL_* flag values.
+ *
  * "grab" names in this file mean, "look at flags to decide whether to use
  * FOLL_PIN or FOLL_GET behavior, when incrementing the page's refcount.
  *
@@ -103,8 +110,14 @@ static inline struct page *try_get_compound_head(struct page *page, int refs)
  * same time. (That's true throughout the get_user_pages*() and
  * pin_user_pages*() APIs.) Cases:
  *
- *    FOLL_GET: page's refcount will be incremented by 1.
- *    FOLL_PIN: page's refcount will be incremented by GUP_PIN_COUNTING_BIAS.
+ *    FOLL_GET: page's refcount will be incremented by @refs.
+ *
+ *    FOLL_PIN on compound pages that are > two pages long: page's refcount will
+ *    be incremented by @refs, and page[2].hpage_pinned_refcount will be
+ *    incremented by @refs * GUP_PIN_COUNTING_BIAS.
+ *
+ *    FOLL_PIN on normal pages, or compound pages that are two pages long:
+ *    page's refcount will be incremented by @refs * GUP_PIN_COUNTING_BIAS.
  *
  * Return: head page (with refcount appropriately incremented) for success, or
  * NULL upon failure. If neither FOLL_GET nor FOLL_PIN was set, that's
@@ -141,6 +154,8 @@ __maybe_unused struct page *try_grab_compound_head(struct page *page,
 		 *
 		 * However, be sure to *also* increment the normal page refcount
 		 * field at least once, so that the page really is pinned.
+		 * That's why the refcount from the earlier
+		 * try_get_compound_head() is left intact.
 		 */
 		if (hpage_pincount_available(page))
 			hpage_pincount_add(page, refs);
@@ -184,10 +199,8 @@ static void put_compound_head(struct page *page, int refs, unsigned int flags)
  * @flags:   gup flags: these are the FOLL_* flag values.
  *
  * Either FOLL_PIN or FOLL_GET (or neither) may be set, but not both at the same
- * time. Cases:
- *
- *    FOLL_GET: page's refcount will be incremented by 1.
- *    FOLL_PIN: page's refcount will be incremented by GUP_PIN_COUNTING_BIAS.
+ * time. Cases: please see the try_grab_compound_head() documentation, with
+ * "refs=1".
  *
  * Return: true for success, or if no action was required (if neither FOLL_PIN
  * nor FOLL_GET was set, nothing is done). False for failure: FOLL_GET or
-- 
2.32.0

[PATCH v2 2/3] mm/gup: small refactoring: simplify try_grab_page()

[John Hubbard]

try_grab_page() does the same thing as try_grab_compound_head(...,
refs=1, ...), just with a different API. So there is a lot of code
duplication there.

Change try_grab_page() to call try_grab_compound_head(), while keeping
the API contract identical for callers.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 mm/gup.c | 31 +++----------------------------
 1 file changed, 3 insertions(+), 28 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 52f08e3177e9..64798d6b5043 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -208,35 +208,10 @@ static void put_compound_head(struct page *page, int refs, unsigned int flags)
  */
 bool __must_check try_grab_page(struct page *page, unsigned int flags)
 {
-	WARN_ON_ONCE((flags & (FOLL_GET | FOLL_PIN)) == (FOLL_GET | FOLL_PIN));
+	if (!(flags & (FOLL_GET | FOLL_PIN)))
+		return true;
 
-	if (flags & FOLL_GET)
-		return try_get_page(page);
-	else if (flags & FOLL_PIN) {
-		int refs = 1;
-
-		page = compound_head(page);
-
-		if (WARN_ON_ONCE(page_ref_count(page) <= 0))
-			return false;
-
-		if (hpage_pincount_available(page))
-			hpage_pincount_add(page, 1);
-		else
-			refs = GUP_PIN_COUNTING_BIAS;
-
-		/*
-		 * Similar to try_grab_compound_head(): even if using the
-		 * hpage_pincount_add/_sub() routines, be sure to
-		 * *also* increment the normal page refcount field at least
-		 * once, so that the page really is pinned.
-		 */
-		page_ref_add(page, refs);
-
-		mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED, 1);
-	}
-
-	return true;
+	return try_grab_compound_head(page, 1, flags) != NULL;
 }
 
 /**
-- 
2.32.0

[PATCH v2 3/3] mm/gup: Remove try_get_page(), call try_get_compound_head() directly

[John Hubbard]

try_get_page() is very similar to try_get_compound_head(), and in fact
try_get_page() has fallen a little behind in terms of maintenance:
try_get_compound_head() handles speculative page references more
thoroughly.

There are only two try_get_page() callsites, so just call
try_get_compound_head() directly from those, and remove try_get_page()
entirely.

Also, seeing as how this changes try_get_compound_head() into a
non-static function, provide some kerneldoc documentation for it.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 arch/s390/mm/fault.c |  2 +-
 fs/pipe.c            |  2 +-
 include/linux/mm.h   | 10 +---------
 mm/gup.c             | 21 +++++++++++++++++----
 4 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 212632d57db9..fe1d2c1dbe3b 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -822,7 +822,7 @@ void do_secure_storage_access(struct pt_regs *regs)
 		break;
 	case KERNEL_FAULT:
 		page = phys_to_page(addr);
-		if (unlikely(!try_get_page(page)))
+		if (unlikely(try_get_compound_head(page, 1) == NULL))
 			break;
 		rc = arch_make_page_accessible(page);
 		put_page(page);
diff --git a/fs/pipe.c b/fs/pipe.c
index 8e6ef62aeb1c..06ba9df37410 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -191,7 +191,7 @@ EXPORT_SYMBOL(generic_pipe_buf_try_steal);
  */
 bool generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
 {
-	return try_get_page(buf->page);
+	return try_get_compound_head(buf->page, 1) != NULL;
 }
 EXPORT_SYMBOL(generic_pipe_buf_get);
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ce8fc0fd6d6e..cd00d1222235 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1207,15 +1207,7 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags);
 __maybe_unused struct page *try_grab_compound_head(struct page *page, int refs,
 						   unsigned int flags);
 
-
-static inline __must_check bool try_get_page(struct page *page)
-{
-	page = compound_head(page);
-	if (WARN_ON_ONCE(page_ref_count(page) <= 0))
-		return false;
-	page_ref_inc(page);
-	return true;
-}
+struct page *try_get_compound_head(struct page *page, int refs);
 
 /**
  * folio_put - Decrement the reference count on a folio.
diff --git a/mm/gup.c b/mm/gup.c
index 64798d6b5043..c2d19d370c99 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -62,11 +62,24 @@ static void put_page_refs(struct page *page, int refs)
 	put_page(page);
 }
 
-/*
- * Return the compound head page with ref appropriately incremented,
- * or NULL if that failed.
+/**
+ * try_get_compound_head() - return the compound head page with refcount
+ * appropriately incremented, or NULL if that failed.
+ *
+ * This handles potential refcount overflow correctly. It also works correctly
+ * for various lockless get_user_pages()-related callers, due to the use of
+ * page_cache_add_speculative().
+ *
+ * Even though the name includes "compound_head", this function is still
+ * appropriate for callers that have a non-compound @page to get.
+ *
+ * @page:  pointer to page to be gotten
+ * @refs:  the value to add to the page's refcount
+ *
+ * Return: head page (with refcount appropriately incremented) for success, or
+ * NULL upon failure.
  */
-static inline struct page *try_get_compound_head(struct page *page, int refs)
+struct page *try_get_compound_head(struct page *page, int refs)
 {
 	struct page *head = compound_head(page);
 
-- 
2.32.0

Re: [PATCH v2 3/3] mm/gup: Remove try_get_page(), call try_get_compound_head() directly

[William Kucharski]

I agree that try_get_page() should probably be removed entirely; is there
a reason you didn't in v2 of the patch?

I'm also curious why you changed try_get_compound_head() into a routine
from an inline.

If you want to retain try_get_page() it should be an inline as well, especially
in its current implementation.

    William Kucharski

> On Aug 11, 2021, at 1:05 AM, John Hubbard <jhubbard@nvidia.com> wrote:
> 
> try_get_page() is very similar to try_get_compound_head(), and in fact
> try_get_page() has fallen a little behind in terms of maintenance:
> try_get_compound_head() handles speculative page references more
> thoroughly.
> 
> There are only two try_get_page() callsites, so just call
> try_get_compound_head() directly from those, and remove try_get_page()
> entirely.
> 
> Also, seeing as how this changes try_get_compound_head() into a
> non-static function, provide some kerneldoc documentation for it.
> 
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Matthew Wilcox <willy@infradead.org>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
> arch/s390/mm/fault.c |  2 +-
> fs/pipe.c            |  2 +-
> include/linux/mm.h   | 10 +---------
> mm/gup.c             | 21 +++++++++++++++++----
> 4 files changed, 20 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> index 212632d57db9..fe1d2c1dbe3b 100644
> --- a/arch/s390/mm/fault.c
> +++ b/arch/s390/mm/fault.c
> @@ -822,7 +822,7 @@ void do_secure_storage_access(struct pt_regs *regs)
> 		break;
> 	case KERNEL_FAULT:
> 		page = phys_to_page(addr);
> -		if (unlikely(!try_get_page(page)))
> +		if (unlikely(try_get_compound_head(page, 1) == NULL))
> 			break;
> 		rc = arch_make_page_accessible(page);
> 		put_page(page);
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 8e6ef62aeb1c..06ba9df37410 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -191,7 +191,7 @@ EXPORT_SYMBOL(generic_pipe_buf_try_steal);
>  */
> bool generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
> {
> -	return try_get_page(buf->page);
> +	return try_get_compound_head(buf->page, 1) != NULL;
> }
> EXPORT_SYMBOL(generic_pipe_buf_get);
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ce8fc0fd6d6e..cd00d1222235 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1207,15 +1207,7 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags);
> __maybe_unused struct page *try_grab_compound_head(struct page *page, int refs,
> 						   unsigned int flags);
> 
> -
> -static inline __must_check bool try_get_page(struct page *page)
> -{
> -	page = compound_head(page);
> -	if (WARN_ON_ONCE(page_ref_count(page) <= 0))
> -		return false;
> -	page_ref_inc(page);
> -	return true;
> -}
> +struct page *try_get_compound_head(struct page *page, int refs);
> 
> /**
>  * folio_put - Decrement the reference count on a folio.
> diff --git a/mm/gup.c b/mm/gup.c
> index 64798d6b5043..c2d19d370c99 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -62,11 +62,24 @@ static void put_page_refs(struct page *page, int refs)
> 	put_page(page);
> }
> 
> -/*
> - * Return the compound head page with ref appropriately incremented,
> - * or NULL if that failed.
> +/**
> + * try_get_compound_head() - return the compound head page with refcount
> + * appropriately incremented, or NULL if that failed.
> + *
> + * This handles potential refcount overflow correctly. It also works correctly
> + * for various lockless get_user_pages()-related callers, due to the use of
> + * page_cache_add_speculative().
> + *
> + * Even though the name includes "compound_head", this function is still
> + * appropriate for callers that have a non-compound @page to get.
> + *
> + * @page:  pointer to page to be gotten
> + * @refs:  the value to add to the page's refcount
> + *
> + * Return: head page (with refcount appropriately incremented) for success, or
> + * NULL upon failure.
>  */
> -static inline struct page *try_get_compound_head(struct page *page, int refs)
> +struct page *try_get_compound_head(struct page *page, int refs)
> {
> 	struct page *head = compound_head(page);
> 
> -- 
> 2.32.0
> 
> 

Re: [PATCH v2 3/3] mm/gup: Remove try_get_page(), call try_get_compound_head() directly

[John Hubbard]

On 8/11/21 1:35 PM, William Kucharski wrote:
> I agree that try_get_page() should probably be removed entirely; is there
> a reason you didn't in v2 of the patch?

Hi William,

This patch *does* remove try_get_page() entirely! Look below. I'll reply
inline, below, to show where that happens.

> 
> I'm also curious why you changed try_get_compound_head() into a routine
> from an inline.

It was part of the change to make it available to callers outside of
gup.c. try_get_compound_head() is slightly messy and doesn't like to
live in mm.h, because it calls page_cache_add_speculative(), which lives
in linux-pagemap.h, which, in turn, has its own set of different headers
that it pulls in.

So, leaving it in gup.c, and exposing it to the other callers as a
non-static function, seemed appropriate here.

> 
> If you want to retain try_get_page() it should be an inline as well, especially
> in its current implementation.
> 
>      William Kucharski
> 
>> On Aug 11, 2021, at 1:05 AM, John Hubbard <jhubbard@nvidia.com> wrote:
>>
>> try_get_page() is very similar to try_get_compound_head(), and in fact
>> try_get_page() has fallen a little behind in terms of maintenance:
>> try_get_compound_head() handles speculative page references more
>> thoroughly.
>>
>> There are only two try_get_page() callsites, so just call
>> try_get_compound_head() directly from those, and remove try_get_page()
>> entirely.
>>
>> Also, seeing as how this changes try_get_compound_head() into a
>> non-static function, provide some kerneldoc documentation for it.
>>
>> Cc: Christoph Hellwig <hch@lst.de>
>> Cc: Matthew Wilcox <willy@infradead.org>
>> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
>> ---
>> arch/s390/mm/fault.c |  2 +-
>> fs/pipe.c            |  2 +-
>> include/linux/mm.h   | 10 +---------
>> mm/gup.c             | 21 +++++++++++++++++----
>> 4 files changed, 20 insertions(+), 15 deletions(-)
>>
>> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
>> index 212632d57db9..fe1d2c1dbe3b 100644
>> --- a/arch/s390/mm/fault.c
>> +++ b/arch/s390/mm/fault.c
>> @@ -822,7 +822,7 @@ void do_secure_storage_access(struct pt_regs *regs)
>> 		break;
>> 	case KERNEL_FAULT:
>> 		page = phys_to_page(addr);
>> -		if (unlikely(!try_get_page(page)))
>> +		if (unlikely(try_get_compound_head(page, 1) == NULL))
>> 			break;
>> 		rc = arch_make_page_accessible(page);
>> 		put_page(page);
>> diff --git a/fs/pipe.c b/fs/pipe.c
>> index 8e6ef62aeb1c..06ba9df37410 100644
>> --- a/fs/pipe.c
>> +++ b/fs/pipe.c
>> @@ -191,7 +191,7 @@ EXPORT_SYMBOL(generic_pipe_buf_try_steal);
>>   */
>> bool generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
>> {
>> -	return try_get_page(buf->page);
>> +	return try_get_compound_head(buf->page, 1) != NULL;
>> }
>> EXPORT_SYMBOL(generic_pipe_buf_get);
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index ce8fc0fd6d6e..cd00d1222235 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -1207,15 +1207,7 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags);
>> __maybe_unused struct page *try_grab_compound_head(struct page *page, int refs,
>> 						   unsigned int flags);
>>
>> -
>> -static inline __must_check bool try_get_page(struct page *page)
>> -{
>> -	page = compound_head(page);
>> -	if (WARN_ON_ONCE(page_ref_count(page) <= 0))
>> -		return false;
>> -	page_ref_inc(page);
>> -	return true;
>> -}

This is where try_get_page() is removed entirely.

thanks,
-- 
John Hubbard
NVIDIA


>> +struct page *try_get_compound_head(struct page *page, int refs);
>>
>> /**
>>   * folio_put - Decrement the reference count on a folio.
>> diff --git a/mm/gup.c b/mm/gup.c
>> index 64798d6b5043..c2d19d370c99 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -62,11 +62,24 @@ static void put_page_refs(struct page *page, int refs)
>> 	put_page(page);
>> }
>>
>> -/*
>> - * Return the compound head page with ref appropriately incremented,
>> - * or NULL if that failed.
>> +/**
>> + * try_get_compound_head() - return the compound head page with refcount
>> + * appropriately incremented, or NULL if that failed.
>> + *
>> + * This handles potential refcount overflow correctly. It also works correctly
>> + * for various lockless get_user_pages()-related callers, due to the use of
>> + * page_cache_add_speculative().
>> + *
>> + * Even though the name includes "compound_head", this function is still
>> + * appropriate for callers that have a non-compound @page to get.
>> + *
>> + * @page:  pointer to page to be gotten
>> + * @refs:  the value to add to the page's refcount
>> + *
>> + * Return: head page (with refcount appropriately incremented) for success, or
>> + * NULL upon failure.
>>   */
>> -static inline struct page *try_get_compound_head(struct page *page, int refs)
>> +struct page *try_get_compound_head(struct page *page, int refs)
>> {
>> 	struct page *head = compound_head(page);
>>
>> -- 
>> 2.32.0
>>
>>
> 
> 

Re: [PATCH v2 3/3] mm/gup: Remove try_get_page(), call try_get_compound_head() directly

[William Kucharski]

> On Aug 11, 2021, at 4:07 PM, John Hubbard <jhubbard@nvidia.com> wrote:
> 
> On 8/11/21 1:35 PM, William Kucharski wrote:
>> I agree that try_get_page() should probably be removed entirely; is there
>> a reason you didn't in v2 of the patch?
> 
> Hi William,
> 
> This patch *does* remove try_get_page() entirely! Look below. I'll reply
> inline, below, to show where that happens.

Ah, my bad.  I was conflating it with try_grab_page() in patch 2/3, which
also seems like it should be an inline, but given your explanation re:
try_get_compound_head() it makes perfect sense.
 
For the series:

Reviewed-by: William Kucharski <william.kucharski@oracle.com>

Re: [PATCH v2 2/3] mm/gup: small refactoring: simplify try_grab_page()

[Christoph Hellwig]

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Note: the __maybe_unused on try_grab_compound_head should be dropped now
that there is always a user.

Re: [PATCH v2 3/3] mm/gup: Remove try_get_page(), call try_get_compound_head() directly

[Christoph Hellwig]

On Wed, Aug 11, 2021 at 12:05:42AM -0700, John Hubbard wrote:
> -		if (unlikely(!try_get_page(page)))
> +		if (unlikely(try_get_compound_head(page, 1) == NULL))

Why not a simple ! instead of the == NULL?

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v2 3/3] mm/gup: Remove try_get_page(), call try_get_compound_head() directly

[John Hubbard]

On 8/12/21 2:22 AM, Christoph Hellwig wrote:
> On Wed, Aug 11, 2021 at 12:05:42AM -0700, John Hubbard wrote:
>> -		if (unlikely(!try_get_page(page)))
>> +		if (unlikely(try_get_compound_head(page, 1) == NULL))
> 
> Why not a simple ! instead of the == NULL?

I'll fix those up and post a v4.

> 
> Otherwise looks good:
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> 

Thanks for the reviews!


thanks,
-- 
John Hubbard
NVIDIA

Re: [PATCH v2 2/3] mm/gup: small refactoring: simplify try_grab_page()

[John Hubbard]

On 8/12/21 2:20 AM, Christoph Hellwig wrote:
> Looks good,
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> 
> Note: the __maybe_unused on try_grab_compound_head should be dropped now
> that there is always a user.


Good point, fixed in v3.


thanks,
-- 
John Hubbard
NVIDIA