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From: John Hubbard <jhubbard@nvidia.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Al Viro" <viro@zeniv.linux.org.uk>,
	"Alex Williamson" <alex.williamson@redhat.com>,
	"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
	"Björn Töpel" <bjorn.topel@intel.com>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Daniel Vetter" <daniel@ffwll.ch>,
	"Dave Chinner" <david@fromorbit.com>,
	"David Airlie" <airlied@linux.ie>,
	"David S . Miller" <davem@davemloft.net>,
	"Ira Weiny" <ira.weiny@intel.com>, "Jan Kara" <jack@suse.cz>,
	"Jason Gunthorpe" <jgg@ziepe.ca>, "Jens Axboe" <axboe@kernel.dk>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Magnus Karlsson" <magnus.karlsson@intel.com>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"Michal Hocko" <mhocko@suse.com>,
	"Mike Kravetz" <mike.kravetz@oracle.com>,
	"Paul Mackerras" <paulus@samba.org>,
	"Shuah Khan" <shuah@kernel.org>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	bpf@vger.kernel.org, dri-devel@lists.freedesktop.org,
	kvm@vger.kernel.org, linux-block@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org,
	linux-rdma@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	netdev@vger.kernel.org, linux-mm@kvack.org,
	LKML <linux-kernel@vger.kernel.org>,
	"John Hubbard" <jhubbard@nvidia.com>,
	"Christoph Hellwig" <hch@lst.de>
Subject: [PATCH v7 05/24] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages
Date: Wed, 20 Nov 2019 23:13:35 -0800
Message-ID: <20191121071354.456618-6-jhubbard@nvidia.com> (raw)
In-Reply-To: <20191121071354.456618-1-jhubbard@nvidia.com>

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(-)

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


  parent reply index

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-21  7:13 [PATCH v7 00/24] mm/gup: track dma-pinned pages: FOLL_PIN John Hubbard
2019-11-21  7:13 ` [PATCH v7 01/24] mm/gup: pass flags arg to __gup_device_* functions John Hubbard
2019-11-21  8:06   ` Christoph Hellwig
2019-11-21  8:25     ` John Hubbard
2019-11-21  7:13 ` [PATCH v7 02/24] mm/gup: factor out duplicate code from four routines John Hubbard
2019-11-21  8:03   ` Christoph Hellwig
2019-11-21  8:29     ` John Hubbard
2019-11-21  9:49       ` Jan Kara
2019-11-21 21:47         ` John Hubbard
2019-11-21  9:54       ` Jan Kara
2019-11-22  2:54         ` John Hubbard
2019-11-22 11:15           ` Jan Kara
2019-11-21  7:13 ` [PATCH v7 03/24] mm/gup: move try_get_compound_head() to top, fix minor issues John Hubbard
2019-11-21  8:07   ` Christoph Hellwig
2019-11-21  7:13 ` [PATCH v7 04/24] mm: Cleanup __put_devmap_managed_page() vs ->page_free() John Hubbard
2019-11-21  8:04   ` Christoph Hellwig
2019-11-21  7:13 ` John Hubbard [this message]
2019-11-21  8:05   ` [PATCH v7 05/24] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages Christoph Hellwig
2019-11-21  8:54     ` John Hubbard
2019-11-21 16:59       ` Dan Williams
2019-11-21 22:22         ` John Hubbard
2019-11-21  7:13 ` [PATCH v7 06/24] goldish_pipe: rename local pin_user_pages() routine John Hubbard
2019-11-21  8:08   ` Christoph Hellwig
2019-11-21  8:36     ` John Hubbard
2019-11-21  7:13 ` [PATCH v7 07/24] IB/umem: use get_user_pages_fast() to pin DMA pages John Hubbard
2019-11-21  8:07   ` Christoph Hellwig
2019-11-21 14:36     ` Jason Gunthorpe
2019-11-24  6:14       ` John Hubbard
2019-11-24 10:07       ` Leon Romanovsky
2019-11-25  0:05         ` John Hubbard
2019-11-25  0:53           ` Jason Gunthorpe
2019-11-21  7:13 ` [PATCH v7 08/24] media/v4l2-core: set pages dirty upon releasing DMA buffers John Hubbard
2019-11-21  8:09   ` Christoph Hellwig
2019-11-21  7:13 ` [PATCH v7 09/24] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM John Hubbard
2019-11-21  8:10   ` Christoph Hellwig
2019-11-21  8:48     ` John Hubbard
2019-11-21 21:35   ` Alex Williamson
2019-11-21 21:49     ` John Hubbard
2019-11-21  7:13 ` [PATCH v7 10/24] mm/gup: introduce pin_user_pages*() and FOLL_PIN John Hubbard
2019-11-21  7:13 ` [PATCH v7 11/24] goldish_pipe: convert to pin_user_pages() and put_user_page() John Hubbard
2019-11-21  7:13 ` [PATCH v7 12/24] IB/{core,hw,umem}: set FOLL_PIN via pin_user_pages*(), fix up ODP John Hubbard
2019-11-21  7:13 ` [PATCH v7 13/24] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote() John Hubbard
2019-11-21  7:13 ` [PATCH v7 14/24] drm/via: set FOLL_PIN via pin_user_pages_fast() John Hubbard
2019-11-21  7:13 ` [PATCH v7 15/24] fs/io_uring: set FOLL_PIN via pin_user_pages() John Hubbard
2019-11-21  7:13 ` [PATCH v7 16/24] net/xdp: " John Hubbard
2019-11-21  7:13 ` [PATCH v7 17/24] mm/gup: track FOLL_PIN pages John Hubbard
2019-11-21  9:39   ` Jan Kara
2019-11-30 18:59   ` kbuild test robot
2019-11-21  7:13 ` [PATCH v7 18/24] media/v4l2-core: pin_user_pages (FOLL_PIN) and put_user_page() conversion John Hubbard
2019-11-21  7:13 ` [PATCH v7 19/24] vfio, mm: " John Hubbard
2019-11-21  7:13 ` [PATCH v7 20/24] powerpc: book3s64: convert to pin_user_pages() and put_user_page() John Hubbard
2019-11-21  7:13 ` [PATCH v7 21/24] mm/gup_benchmark: use proper FOLL_WRITE flags instead of hard-coding "1" John Hubbard
2019-11-21  7:13 ` [PATCH v7 22/24] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2019-11-21  7:13 ` [PATCH v7 23/24] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
2019-11-21  7:13 ` [PATCH v7 24/24] mm, tree-wide: rename put_user_page*() to unpin_user_page*() John Hubbard

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