diff mbox series

[v7,05/24] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages

Message ID 20191121071354.456618-6-jhubbard@nvidia.com (mailing list archive)
State New, archived
Headers show
Series mm/gup: track dma-pinned pages: FOLL_PIN | expand

Commit Message

John Hubbard Nov. 21, 2019, 7:13 a.m. UTC 
An upcoming patch changes and complicates the refcounting and
especially the "put page" aspects of it. In order to keep
everything clean, refactor the devmap page release routines:

* Rename put_devmap_managed_page() to page_is_devmap_managed(),
  and limit the functionality to "read only": return a bool,
  with no side effects.

* Add a new routine, put_devmap_managed_page(), to handle checking
  what kind of page it is, and what kind of refcount handling it
  requires.

* Rename __put_devmap_managed_page() to free_devmap_managed_page(),
  and limit the functionality to unconditionally freeing a devmap
  page.

This is originally based on a separate patch by Ira Weiny, which
applied to an early version of the put_user_page() experiments.
Since then, Jérôme Glisse suggested the refactoring described above.

Cc: Christoph Hellwig <hch@lst.de>
Suggested-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 include/linux/mm.h | 27 ++++++++++++++++++++++++---
 mm/memremap.c      | 16 ++--------------
 2 files changed, 26 insertions(+), 17 deletions(-)

Comments

Christoph Hellwig Nov. 21, 2019, 8:05 a.m. UTC | #1 
So while this looks correct and I still really don't see the major
benefit of the new code organization, especially as it bloats all
put_page callers.

I'd love to see code size change stats for an allyesconfig on this
commit.
John Hubbard Nov. 21, 2019, 8:54 a.m. UTC | #2 
On 11/21/19 12:05 AM, Christoph Hellwig wrote:
> So while this looks correct and I still really don't see the major
> benefit of the new code organization, especially as it bloats all
> put_page callers.
> 
> I'd love to see code size change stats for an allyesconfig on this
> commit.
> 

Right, I'm running that now, will post the results. (btw, if there is
a script and/or standard format I should use, I'm all ears. I'll dig
through lwn...)



thanks,
Dan Williams Nov. 21, 2019, 4:59 p.m. UTC | #3 
On Thu, Nov 21, 2019 at 12:57 AM John Hubbard <jhubbard@nvidia.com> wrote:
>
> On 11/21/19 12:05 AM, Christoph Hellwig wrote:
> > So while this looks correct and I still really don't see the major
> > benefit of the new code organization, especially as it bloats all
> > put_page callers.
> >
> > I'd love to see code size change stats for an allyesconfig on this
> > commit.
> >
>
> Right, I'm running that now, will post the results. (btw, if there is
> a script and/or standard format I should use, I'm all ears. I'll dig
> through lwn...)
>

Just run:

    size vmlinux
John Hubbard Nov. 21, 2019, 10:22 p.m. UTC | #4 
On 11/21/19 8:59 AM, Dan Williams wrote:
> On Thu, Nov 21, 2019 at 12:57 AM John Hubbard <jhubbard@nvidia.com> wrote:
>>
>> On 11/21/19 12:05 AM, Christoph Hellwig wrote:
>>> So while this looks correct and I still really don't see the major
>>> benefit of the new code organization, especially as it bloats all
>>> put_page callers.
>>>
>>> I'd love to see code size change stats for an allyesconfig on this
>>> commit.
>>>
>>
>> Right, I'm running that now, will post the results. (btw, if there is
>> a script and/or standard format I should use, I'm all ears. I'll dig
>> through lwn...)
>>
> 
> Just run:
> 
>      size vmlinux
> 

Beautiful. I thought it would involve a lot more. Here's results:

linux.git (Linux 5.4-rc8+):
==============================================
   text	   data	    bss	    dec	    hex	filename
227578032	213267935	76877984	517723951	1edbd72f	vmlinux


With patches 4 and 5 applied to linux.git:
==========================================
   text	   data	    bss	    dec	    hex	filename
229698560	213288379	76853408	519840347	1efc225b	vmlinux


Analysis:
=========

This increased the size of text by 0.93%. Which is a measurable bloat, so
the inlining really is undesirable here, yes. I'll do it differently.

thanks,
diff mbox series

Patch

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a2adf95b3f9c..96228376139c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -967,9 +967,10 @@  static inline bool is_zone_device_page(const struct page *page)
 #endif
 
 #ifdef CONFIG_DEV_PAGEMAP_OPS
-void __put_devmap_managed_page(struct page *page);
+void free_devmap_managed_page(struct page *page);
 DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
-static inline bool put_devmap_managed_page(struct page *page)
+
+static inline bool page_is_devmap_managed(struct page *page)
 {
 	if (!static_branch_unlikely(&devmap_managed_key))
 		return false;
@@ -978,7 +979,6 @@  static inline bool put_devmap_managed_page(struct page *page)
 	switch (page->pgmap->type) {
 	case MEMORY_DEVICE_PRIVATE:
 	case MEMORY_DEVICE_FS_DAX:
-		__put_devmap_managed_page(page);
 		return true;
 	default:
 		break;
@@ -986,6 +986,27 @@  static inline bool put_devmap_managed_page(struct page *page)
 	return false;
 }
 
+static inline bool put_devmap_managed_page(struct page *page)
+{
+	bool is_devmap = page_is_devmap_managed(page);
+
+	if (is_devmap) {
+		int count = page_ref_dec_return(page);
+
+		/*
+		 * devmap page refcounts are 1-based, rather than 0-based: if
+		 * refcount is 1, then the page is free and the refcount is
+		 * stable because nobody holds a reference on the page.
+		 */
+		if (count == 1)
+			free_devmap_managed_page(page);
+		else if (!count)
+			__put_page(page);
+	}
+
+	return is_devmap;
+}
+
 #else /* CONFIG_DEV_PAGEMAP_OPS */
 static inline bool put_devmap_managed_page(struct page *page)
 {
diff --git a/mm/memremap.c b/mm/memremap.c
index e899fa876a62..2ba773859031 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -411,20 +411,8 @@  struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
 EXPORT_SYMBOL_GPL(get_dev_pagemap);
 
 #ifdef CONFIG_DEV_PAGEMAP_OPS
-void __put_devmap_managed_page(struct page *page)
+void free_devmap_managed_page(struct page *page)
 {
-	int count = page_ref_dec_return(page);
-
-	/* still busy */
-	if (count > 1)
-		return;
-
-	/* only triggered by the dev_pagemap shutdown path */
-	if (count == 0) {
-		__put_page(page);
-		return;
-	}
-
 	/* notify page idle for dax */
 	if (!is_device_private_page(page)) {
 		wake_up_var(&page->_refcount);
@@ -461,5 +449,5 @@  void __put_devmap_managed_page(struct page *page)
 	page->mapping = NULL;
 	page->pgmap->ops->page_free(page);
 }
-EXPORT_SYMBOL(__put_devmap_managed_page);
+EXPORT_SYMBOL(free_devmap_managed_page);
 #endif /* CONFIG_DEV_PAGEMAP_OPS */