[PATCH 12/15] mm, dax: enable filesystems to trigger page-idle callbacks

From: Dan Williams
Date: Tue Oct 31 2017 - 19:29:14 EST

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Towards solving DAX-DMA vs truncate arrange for filesystems to set up a
page-idle callback when they mount a dax_device.

No functional changes are expected as this only registers a nop handler
for the ->page_free() event for device-mapped pages.

Cc: "JÃrÃme Glisse" <jglisse@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
drivers/dax/super.c | 80 ++++++++++++++++++++++++++++++++++++++++------
drivers/nvdimm/pmem.c | 13 +++++++
fs/ext2/super.c | 6 ++-
fs/ext4/super.c | 6 ++-
fs/xfs/xfs_super.c | 20 ++++++------
include/linux/dax.h | 17 +++++-----
include/linux/memremap.h | 6 +++
kernel/memremap.c | 1 +
8 files changed, 113 insertions(+), 36 deletions(-)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 3ccb064d200d..193e0cd8d90c 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -29,6 +29,7 @@ static struct vfsmount *dax_mnt;
static DEFINE_IDA(dax_minor_ida);
static struct kmem_cache *dax_cache __read_mostly;
static struct super_block *dax_superblock __read_mostly;
+DEFINE_MUTEX(devmap_lock);

#define DAX_HASH_SIZE (PAGE_SIZE / sizeof(struct hlist_head))
static struct hlist_head dax_host_list[DAX_HASH_SIZE];
@@ -62,16 +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
@@ -169,9 +160,65 @@ struct dax_device {
const char *host;
void *private;
unsigned long flags;
+ struct dev_pagemap *pgmap;
const struct dax_operations *ops;
};

+#if IS_ENABLED(CONFIG_FS_DAX)
+static void generic_dax_pagefree(struct page *page, void *data)
+{
+}
+
+struct dax_device *fs_dax_claim_bdev(struct block_device *bdev, void *owner)
+{
+ struct dax_device *dax_dev;
+ struct dev_pagemap *pgmap;
+
+ if (!blk_queue_dax(bdev->bd_queue))
+ return NULL;
+ dax_dev = fs_dax_get_by_host(bdev->bd_disk->disk_name);
+ if (!dax_dev->pgmap)
+ return dax_dev;
+ pgmap = dax_dev->pgmap;
+
+ mutex_lock(&devmap_lock);
+ if ((pgmap->data && pgmap->data != owner) || pgmap->page_free
+ || pgmap->page_fault
+ || pgmap->type != MEMORY_DEVICE_HOST) {
+ put_dax(dax_dev);
+ mutex_unlock(&devmap_lock);
+ return NULL;
+ }
+
+ pgmap->type = MEMORY_DEVICE_FS_DAX;
+ pgmap->page_free = generic_dax_pagefree;
+ pgmap->data = owner;
+ mutex_unlock(&devmap_lock);
+
+ return dax_dev;
+}
+EXPORT_SYMBOL_GPL(fs_dax_claim_bdev);
+
+void fs_dax_release(struct dax_device *dax_dev, void *owner)
+{
+ struct dev_pagemap *pgmap = dax_dev ? dax_dev->pgmap : NULL;
+
+ put_dax(dax_dev);
+ if (!pgmap)
+ return;
+ if (!pgmap->data)
+ return;
+
+ mutex_lock(&devmap_lock);
+ WARN_ON(pgmap->data != owner);
+ pgmap->type = MEMORY_DEVICE_HOST;
+ pgmap->page_free = NULL;
+ pgmap->data = NULL;
+ mutex_unlock(&devmap_lock);
+}
+EXPORT_SYMBOL_GPL(fs_dax_release);
+#endif
+
static ssize_t write_cache_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
@@ -502,10 +549,23 @@ 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)
return;
+ put_dev_pagemap(dax_dev->pgmap);
+ dax_dev->pgmap = NULL;
iput(&dax_dev->inode);
}
EXPORT_SYMBOL_GPL(put_dax);
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 39dfd7affa31..9f36a2193eb6 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -300,6 +300,7 @@ static int pmem_attach_disk(struct device *dev,
struct vmem_altmap __altmap, *altmap = NULL;
int nid = dev_to_node(dev), fua, wbc;
struct resource *res = &nsio->res;
+ struct dev_pagemap *pgmap = NULL;
struct nd_pfn *nd_pfn = NULL;
struct dax_device *dax_dev;
struct nd_pfn_sb *pfn_sb;
@@ -358,14 +359,24 @@ static int pmem_attach_disk(struct device *dev,
pmem->pfn_flags |= PFN_MAP;
res = &pfn_res; /* for badblocks populate */
res->start += pmem->data_offset;
+ pgmap = get_dev_pagemap(PHYS_PFN(virt_to_phys(addr)), NULL);
+ if (!pgmap)
+ return -ENOMEM;
} else if (pmem_should_map_pages(dev)) {
addr = devm_memremap_pages(dev, &nsio->res,
&q->q_usage_counter, NULL);
pmem->pfn_flags |= PFN_MAP;
+ pgmap = get_dev_pagemap(PHYS_PFN(virt_to_phys(addr)), NULL);
+ if (!pgmap)
+ return -ENOMEM;
} else
addr = devm_memremap(dev, pmem->phys_addr,
pmem->size, ARCH_MEMREMAP_PMEM);

+
+ /* we still hold a reference until the driver is unloaded */
+ put_dev_pagemap(pgmap);
+
/*
* At release time the queue must be frozen before
* devm_memremap_pages is unwound
@@ -402,7 +413,7 @@ static int pmem_attach_disk(struct device *dev,
nvdimm_badblocks_populate(nd_region, &pmem->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, pgmap);
if (!dax_dev) {
put_disk(disk);
return -ENOMEM;
diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 1458706bd2ec..884784acd9fd 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -171,7 +171,7 @@ 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);
}

@@ -814,7 +814,7 @@ 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;
@@ -1202,7 +1202,7 @@ 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 b104096fce9e..f27355f41616 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -950,7 +950,7 @@ 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);
}

@@ -3397,7 +3397,7 @@ 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;
@@ -4400,7 +4400,7 @@ 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 584cf2d573ba..fdc4785a5c85 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -722,7 +722,7 @@ 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;
@@ -730,10 +730,10 @@ 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);
}

/*
@@ -751,9 +751,9 @@ 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;

/*
@@ -763,7 +763,7 @@ 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) {
@@ -777,7 +777,7 @@ 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);
}

/*
@@ -811,14 +811,14 @@ 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 122197124b9d..ea21ebfd1889 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -50,12 +50,8 @@ 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);
#else
static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
{
@@ -67,13 +63,14 @@ 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;
}
#endif

@@ -81,6 +78,8 @@ int dax_read_lock(void);
void dax_read_unlock(int id);
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);
bool dax_alive(struct dax_device *dax_dev);
void kill_dax(struct dax_device *dax_dev);
void *dax_get_private(struct dax_device *dax_dev);
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 79f8ba7c3894..39d2de3f744b 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -64,11 +64,17 @@ static inline struct vmem_altmap *to_vmem_altmap(unsigned long memmap_start)
* driver can hotplug the device memory using ZONE_DEVICE and with that memory
* type. Any page of a process can be migrated to such memory. However no one
* should be allow to pin such memory so that it can always be evicted.
+ *
+ * MEMORY_DEVICE_FS_DAX:
+ * MEMORY_DEVICE_HOST memory that is being managed by a filesystem. The
+ * filesystem needs page idle callbacks to coordinate direct-I/O + DMA
+ * (get_user_pages) vs truncate.
*/
enum memory_type {
MEMORY_DEVICE_HOST = 0,
MEMORY_DEVICE_PRIVATE,
MEMORY_DEVICE_PUBLIC,
+ MEMORY_DEVICE_FS_DAX,
};

/*
diff --git a/kernel/memremap.c b/kernel/memremap.c
index 403ab9cdb949..bf61cfa89c7d 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -323,6 +323,7 @@ struct dev_pagemap *find_dev_pagemap(resource_size_t phys)
page_map = radix_tree_lookup(&pgmap_radix, PHYS_PFN(phys));
return page_map ? &page_map->pgmap : NULL;
}
+EXPORT_SYMBOL_GPL(find_dev_pagemap);

/**
* devm_memremap_pages - remap and provide memmap backing for the given resource

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