[RFC 06/10] fs/dax: Add dax_page_free callback

[Alistair Popple <apopple@nvidia.com>]

When a fs dax page is freed it has to notify filesystems that the page
has been unpinned/unmapped and is free. Currently this involves
special code in the page free paths to detect a transition of refcount
from 2 to 1 and to call some fs dax specific code.

A future change will require this to happen when the page refcount
drops to zero. In this case we can use the existing
pgmap->ops->page_free() callback so wire that up for all devices that
support FS DAX (nvdimm and virtio).

Signed-off-by: Alistair Popple <apopple@nvidia.com>
---
 drivers/nvdimm/pmem.c | 1 +
 fs/dax.c              | 6 ++++++
 fs/fuse/virtio_fs.c   | 5 +++++
 include/linux/dax.h   | 1 +
 4 files changed, 13 insertions(+)

diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 4e8fdcb..b027e1f 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -444,6 +444,7 @@ static int pmem_pagemap_memory_failure(struct dev_pagemap *pgmap,
 
 static const struct dev_pagemap_ops fsdax_pagemap_ops = {
 	.memory_failure		= pmem_pagemap_memory_failure,
+	.page_free      	= dax_page_free,
 };
 
 static int pmem_attach_disk(struct device *dev,
diff --git a/fs/dax.c b/fs/dax.c
index a7bd423..17b1c5f 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1981,3 +1981,9 @@ int dax_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 					       pos_out, len, remap_flags, ops);
 }
 EXPORT_SYMBOL_GPL(dax_remap_file_range_prep);
+
+void dax_page_free(struct page *page)
+{
+	wake_up_var(page);
+}
+EXPORT_SYMBOL_GPL(dax_page_free);
diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index 5f1be1d..11bfc28 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -795,6 +795,10 @@ static void virtio_fs_cleanup_dax(void *data)
 	put_dax(dax_dev);
 }
 
+static const struct dev_pagemap_ops fsdax_pagemap_ops = {
+	.page_free = dax_page_free,
+};
+
 static int virtio_fs_setup_dax(struct virtio_device *vdev, struct virtio_fs *fs)
 {
 	struct virtio_shm_region cache_reg;
@@ -827,6 +831,7 @@ static int virtio_fs_setup_dax(struct virtio_device *vdev, struct virtio_fs *fs)
 		return -ENOMEM;
 
 	pgmap->type = MEMORY_DEVICE_FS_DAX;
+	pgmap->ops = &fsdax_pagemap_ops;
 
 	/* Ideally we would directly use the PCI BAR resource but
 	 * devm_memremap_pages() wants its own copy in pgmap.  So
diff --git a/include/linux/dax.h b/include/linux/dax.h
index bced4d4..c0c3206 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -212,6 +212,7 @@ int dax_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
 int dax_truncate_page(struct inode *inode, loff_t pos, bool *did_zero,
 		const struct iomap_ops *ops);
 
+void dax_page_free(struct page *page);
 static inline int dax_wait_page_idle(struct page *page,
 				void (cb)(struct inode *),
 				struct inode *inode)
-- 
git-series 0.9.1