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Message-ID: <20191121071354.456618-6-jhubbard@nvidia.com>
Date: Wed, 20 Nov 2019 23:13:35 -0800
From: John Hubbard <jhubbard@...dia.com>
To: Andrew Morton <akpm@...ux-foundation.org>
CC: Al Viro <viro@...iv.linux.org.uk>,
Alex Williamson <alex.williamson@...hat.com>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Björn Töpel <bjorn.topel@...el.com>,
Christoph Hellwig <hch@...radead.org>,
Dan Williams <dan.j.williams@...el.com>,
Daniel Vetter <daniel@...ll.ch>,
Dave Chinner <david@...morbit.com>,
David Airlie <airlied@...ux.ie>,
"David S . Miller" <davem@...emloft.net>,
Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
Jonathan Corbet <corbet@....net>,
Jérôme Glisse <jglisse@...hat.com>,
Magnus Karlsson <magnus.karlsson@...el.com>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
Michael Ellerman <mpe@...erman.id.au>,
Michal Hocko <mhocko@...e.com>,
Mike Kravetz <mike.kravetz@...cle.com>,
Paul Mackerras <paulus@...ba.org>,
Shuah Khan <shuah@...nel.org>,
Vlastimil Babka <vbabka@...e.cz>, <bpf@...r.kernel.org>,
<dri-devel@...ts.freedesktop.org>, <kvm@...r.kernel.org>,
<linux-block@...r.kernel.org>, <linux-doc@...r.kernel.org>,
<linux-fsdevel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
<linux-media@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
<linuxppc-dev@...ts.ozlabs.org>, <netdev@...r.kernel.org>,
<linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
John Hubbard <jhubbard@...dia.com>,
Christoph Hellwig <hch@....de>
Subject: [PATCH v7 05/24] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages
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@....de>
Suggested-by: Jérôme Glisse <jglisse@...hat.com>
Reviewed-by: Dan Williams <dan.j.williams@...el.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Signed-off-by: Ira Weiny <ira.weiny@...el.com>
Signed-off-by: John Hubbard <jhubbard@...dia.com>
---
include/linux/mm.h | 27 ++++++++++++++++++++++++---
mm/memremap.c | 16 ++--------------
2 files changed, 26 insertions(+), 17 deletions(-)
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 */
--
2.24.0
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