linux-kernel - [PATCH] mm: Cleanup __put_devmap_managed_page() vs ->page

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Date:   Wed, 13 Nov 2019 16:07:22 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     jhubbard@...dia.com
Cc:     Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
        Ira Weiny <ira.weiny@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        linux-nvdimm@...ts.01.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: [PATCH] mm: Cleanup __put_devmap_managed_page() vs ->page_free()

After the removal of the device-public infrastructure there are only 2
->page_free() call backs in the kernel. One of those is a device-private
callback in the nouveau driver, the other is a generic wakeup needed in
the DAX case. In the hopes that all ->page_free() callbacks can be
migrated to common core kernel functionality, move the device-private
specific actions in __put_devmap_managed_page() under the
is_device_private_page() conditional, including the ->page_free()
callback. For the other page types just open-code the generic wakeup.

Yes, the wakeup is only needed in the MEMORY_DEVICE_FSDAX case, but it
does no harm in the MEMORY_DEVICE_DEVDAX and MEMORY_DEVICE_PCI_P2PDMA
case.

Cc: Jan Kara <jack@...e.cz>
Cc: Christoph Hellwig <hch@....de>
Cc: Ira Weiny <ira.weiny@...el.com>
Cc: Jérôme Glisse <jglisse@...hat.com>
Cc: John Hubbard <jhubbard@...dia.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
Hi John,

This applies on top of today's linux-next and passes my nvdimm unit
tests. That testing noticed that devmap_managed_enable_get() needed a
small fixup as well.

 drivers/nvdimm/pmem.c |    6 ------
 mm/memremap.c         |   22 ++++++++++++----------
 2 files changed, 12 insertions(+), 16 deletions(-)

diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index f9f76f6ba07b..21db1ce8c0ae 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -338,13 +338,7 @@ static void pmem_release_disk(void *__pmem)
 	put_disk(pmem->disk);
 }
 
-static void pmem_pagemap_page_free(struct page *page)
-{
-	wake_up_var(&page->_refcount);
-}
-
 static const struct dev_pagemap_ops fsdax_pagemap_ops = {
-	.page_free		= pmem_pagemap_page_free,
 	.kill			= pmem_pagemap_kill,
 	.cleanup		= pmem_pagemap_cleanup,
 };
diff --git a/mm/memremap.c b/mm/memremap.c
index 022e78e68ea0..6e6f3d6fdb73 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -27,7 +27,8 @@ static void devmap_managed_enable_put(void)
 
 static int devmap_managed_enable_get(struct dev_pagemap *pgmap)
 {
-	if (!pgmap->ops || !pgmap->ops->page_free) {
+	if (!pgmap->ops || (pgmap->type == MEMORY_DEVICE_PRIVATE
+				&& !pgmap->ops->page_free)) {
 		WARN(1, "Missing page_free method\n");
 		return -EINVAL;
 	}
@@ -449,12 +450,6 @@ void __put_devmap_managed_page(struct page *page)
 	 * holds a reference on the page.
 	 */
 	if (count == 1) {
-		/* Clear Active bit in case of parallel mark_page_accessed */
-		__ClearPageActive(page);
-		__ClearPageWaiters(page);
-
-		mem_cgroup_uncharge(page);
-
 		/*
 		 * When a device_private page is freed, the page->mapping field
 		 * may still contain a (stale) mapping value. For example, the
@@ -476,10 +471,17 @@ void __put_devmap_managed_page(struct page *page)
 		 * handled differently or not done at all, so there is no need
 		 * to clear page->mapping.
 		 */
-		if (is_device_private_page(page))
-			page->mapping = NULL;
+		if (is_device_private_page(page)) {
+			/* Clear Active bit in case of parallel mark_page_accessed */
+			__ClearPageActive(page);
+			__ClearPageWaiters(page);
 
-		page->pgmap->ops->page_free(page);
+			mem_cgroup_uncharge(page);
+
+			page->mapping = NULL;
+			page->pgmap->ops->page_free(page);
+		} else
+			wake_up_var(&page->_refcount);
 	} else if (!count)
 		__put_page(page);
 }