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Subject[PATCH v8 11/18] mm, dax: enable filesystems to trigger dev_pagemap ->page_free callbacks
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In order to resolve collisions between filesystem operations and DMA to
DAX mapped pages we need a callback when DMA completes. With a callback
we can hold off filesystem operations while DMA is in-flight and then
resume those operations when the last put_page() occurs on a DMA page.

Recall that the 'struct page' entries for DAX memory are created with
devm_memremap_pages(). That routine arranges for the pages to be
allocated, but never onlined, so a DAX page is DMA-idle when its
reference count reaches one.

Also recall that the HMM sub-system added infrastructure to trap the
page-idle (2-to-1 reference count) transition of the pages allocated by
devm_memremap_pages() and trigger a callback via the 'struct
dev_pagemap' associated with the page range. Whereas the HMM callbacks
are going to a device driver to manage bounce pages in device-memory in
the filesystem-dax case we will call back to filesystem specified
callback.

Since the callback is not known at devm_memremap_pages() time we arrange
for the filesystem to install it at mount time. No functional changes
are expected as this only registers a nop handler for the ->page_free()
event for device-mapped pages.

Cc: Michal Hocko <mhocko@suse.com>
Reviewed-by: "Jérôme Glisse" <jglisse@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/dax/super.c | 21 +++++++++++----------
drivers/nvdimm/pmem.c | 3 ++-
fs/ext2/super.c | 6 +++---
fs/ext4/super.c | 6 +++---
fs/xfs/xfs_super.c | 20 ++++++++++----------
include/linux/dax.h | 23 ++++++++++++++---------
6 files changed, 43 insertions(+), 36 deletions(-)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index c4cf284dfe1c..7d260f118a39 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -63,16 +63,6 @@ int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
}
EXPORT_SYMBOL(bdev_dax_pgoff);

-#if IS_ENABLED(CONFIG_FS_DAX)
-struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
-{
- if (!blk_queue_dax(bdev->bd_queue))
- return NULL;
- return fs_dax_get_by_host(bdev->bd_disk->disk_name);
-}
-EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);
-#endif
-
/**
* __bdev_dax_supported() - Check if the device supports dax for filesystem
* @sb: The superblock of the device
@@ -579,6 +569,17 @@ struct dax_device *alloc_dax(void *private, const char *__host,
}
EXPORT_SYMBOL_GPL(alloc_dax);

+struct dax_device *alloc_dax_devmap(void *private, const char *host,
+ const struct dax_operations *ops, struct dev_pagemap *pgmap)
+{
+ struct dax_device *dax_dev = alloc_dax(private, host, ops);
+
+ if (dax_dev)
+ dax_dev->pgmap = pgmap;
+ return dax_dev;
+}
+EXPORT_SYMBOL_GPL(alloc_dax_devmap);
+
void put_dax(struct dax_device *dax_dev)
{
if (!dax_dev)
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 06f8dcc52ca6..e6d7351f3379 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -408,7 +408,8 @@ static int pmem_attach_disk(struct device *dev,
nvdimm_badblocks_populate(nd_region, &pmem->bb, &bb_res);
disk->bb = &pmem->bb;

- dax_dev = alloc_dax(pmem, disk->disk_name, &pmem_dax_ops);
+ dax_dev = alloc_dax_devmap(pmem, disk->disk_name, &pmem_dax_ops,
+ &pmem->pgmap);
if (!dax_dev) {
put_disk(disk);
return -ENOMEM;
diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 7666c065b96f..6ae20e319bc4 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -172,7 +172,7 @@ static void ext2_put_super (struct super_block * sb)
brelse (sbi->s_sbh);
sb->s_fs_info = NULL;
kfree(sbi->s_blockgroup_lock);
- fs_put_dax(sbi->s_daxdev);
+ fs_dax_release(sbi->s_daxdev, sb);
kfree(sbi);
}

@@ -817,7 +817,7 @@ static unsigned long descriptor_loc(struct super_block *sb,

static int ext2_fill_super(struct super_block *sb, void *data, int silent)
{
- struct dax_device *dax_dev = fs_dax_get_by_bdev(sb->s_bdev);
+ struct dax_device *dax_dev = fs_dax_claim_bdev(sb->s_bdev, sb);
struct buffer_head * bh;
struct ext2_sb_info * sbi;
struct ext2_super_block * es;
@@ -1213,7 +1213,7 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
kfree(sbi->s_blockgroup_lock);
kfree(sbi);
failed:
- fs_put_dax(dax_dev);
+ fs_dax_release(dax_dev, sb);
return ret;
}

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 39bf464c35f1..315a323729e3 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -952,7 +952,7 @@ static void ext4_put_super(struct super_block *sb)
if (sbi->s_chksum_driver)
crypto_free_shash(sbi->s_chksum_driver);
kfree(sbi->s_blockgroup_lock);
- fs_put_dax(sbi->s_daxdev);
+ fs_dax_release(sbi->s_daxdev, sb);
kfree(sbi);
}

@@ -3398,7 +3398,7 @@ static void ext4_set_resv_clusters(struct super_block *sb)

static int ext4_fill_super(struct super_block *sb, void *data, int silent)
{
- struct dax_device *dax_dev = fs_dax_get_by_bdev(sb->s_bdev);
+ struct dax_device *dax_dev = fs_dax_claim_bdev(sb->s_bdev, sb);
char *orig_data = kstrdup(data, GFP_KERNEL);
struct buffer_head *bh;
struct ext4_super_block *es = NULL;
@@ -4408,7 +4408,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
out_free_base:
kfree(sbi);
kfree(orig_data);
- fs_put_dax(dax_dev);
+ fs_dax_release(dax_dev, sb);
return err ? err : ret;
}

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 93588ea3d3d2..ef7dd7148c0b 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -724,7 +724,7 @@ xfs_close_devices(

xfs_free_buftarg(mp, mp->m_logdev_targp);
xfs_blkdev_put(logdev);
- fs_put_dax(dax_logdev);
+ fs_dax_release(dax_logdev, mp);
}
if (mp->m_rtdev_targp) {
struct block_device *rtdev = mp->m_rtdev_targp->bt_bdev;
@@ -732,10 +732,10 @@ xfs_close_devices(

xfs_free_buftarg(mp, mp->m_rtdev_targp);
xfs_blkdev_put(rtdev);
- fs_put_dax(dax_rtdev);
+ fs_dax_release(dax_rtdev, mp);
}
xfs_free_buftarg(mp, mp->m_ddev_targp);
- fs_put_dax(dax_ddev);
+ fs_dax_release(dax_ddev, mp);
}

/*
@@ -753,9 +753,9 @@ xfs_open_devices(
struct xfs_mount *mp)
{
struct block_device *ddev = mp->m_super->s_bdev;
- struct dax_device *dax_ddev = fs_dax_get_by_bdev(ddev);
- struct dax_device *dax_logdev = NULL, *dax_rtdev = NULL;
+ struct dax_device *dax_ddev = fs_dax_claim_bdev(ddev, mp);
struct block_device *logdev = NULL, *rtdev = NULL;
+ struct dax_device *dax_logdev = NULL, *dax_rtdev = NULL;
int error;

/*
@@ -765,7 +765,7 @@ xfs_open_devices(
error = xfs_blkdev_get(mp, mp->m_logname, &logdev);
if (error)
goto out;
- dax_logdev = fs_dax_get_by_bdev(logdev);
+ dax_logdev = fs_dax_claim_bdev(logdev, mp);
}

if (mp->m_rtname) {
@@ -779,7 +779,7 @@ xfs_open_devices(
error = -EINVAL;
goto out_close_rtdev;
}
- dax_rtdev = fs_dax_get_by_bdev(rtdev);
+ dax_rtdev = fs_dax_claim_bdev(rtdev, mp);
}

/*
@@ -813,14 +813,14 @@ xfs_open_devices(
xfs_free_buftarg(mp, mp->m_ddev_targp);
out_close_rtdev:
xfs_blkdev_put(rtdev);
- fs_put_dax(dax_rtdev);
+ fs_dax_release(dax_rtdev, mp);
out_close_logdev:
if (logdev && logdev != ddev) {
xfs_blkdev_put(logdev);
- fs_put_dax(dax_logdev);
+ fs_dax_release(dax_logdev, mp);
}
out:
- fs_put_dax(dax_ddev);
+ fs_dax_release(dax_ddev, mp);
return error;
}

diff --git a/include/linux/dax.h b/include/linux/dax.h
index e9d59a6b06e1..a88ff009e2a1 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -32,6 +32,8 @@ extern struct attribute_group dax_attribute_group;
struct dax_device *dax_get_by_host(const char *host);
struct dax_device *alloc_dax(void *private, const char *host,
const struct dax_operations *ops);
+struct dax_device *alloc_dax_devmap(void *private, const char *host,
+ const struct dax_operations *ops, struct dev_pagemap *pgmap);
void put_dax(struct dax_device *dax_dev);
void kill_dax(struct dax_device *dax_dev);
void dax_write_cache(struct dax_device *dax_dev, bool wc);
@@ -50,6 +52,12 @@ static inline struct dax_device *alloc_dax(void *private, const char *host,
*/
return NULL;
}
+static inline struct dax_device *alloc_dax_devmap(void *private,
+ const char *host, const struct dax_operations *ops,
+ struct dev_pagemap *pgmap)
+{
+ return NULL;
+}
static inline void put_dax(struct dax_device *dax_dev)
{
}
@@ -79,12 +87,8 @@ static inline struct dax_device *fs_dax_get_by_host(const char *host)
return dax_get_by_host(host);
}

-static inline void fs_put_dax(struct dax_device *dax_dev)
-{
- put_dax(dax_dev);
-}
-
-struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev);
+struct dax_device *fs_dax_claim_bdev(struct block_device *bdev, void *owner);
+void fs_dax_release(struct dax_device *dax_dev, void *owner);
int dax_writeback_mapping_range(struct address_space *mapping,
struct block_device *bdev, struct writeback_control *wbc);
struct dax_device *fs_dax_claim(struct dax_device *dax_dev, void *owner);
@@ -100,13 +104,14 @@ static inline struct dax_device *fs_dax_get_by_host(const char *host)
return NULL;
}

-static inline void fs_put_dax(struct dax_device *dax_dev)
+static inline struct dax_device *fs_dax_claim_bdev(struct block_device *bdev,
+ void *owner)
{
+ return NULL;
}

-static inline struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
+static inline void fs_dax_release(struct dax_device *dax_dev, void *owner)
{
- return NULL;
}

static inline int dax_writeback_mapping_range(struct address_space *mapping,
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